Next Article in Journal
Sustainable Careers of Athletes: Themes and Concepts Regarding Transition Theories Involving Athletes
Next Article in Special Issue
Electrospun Nanofibre Air Filters for Particles and Gaseous Pollutants
Previous Article in Journal
Integrated Evaluation of Changing Water Resources in an Active Ecotourism Area: The Case of Puerto Princesa City, Palawan, Philippines
Previous Article in Special Issue
Sensitivity Analysis of Envelope Design Parameters of Industrial Buildings with Natural Ventilation
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Sustainability
Volume 13
Issue 9
10.3390/su13094821
sustainability-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Formation of Formaldehyde and Other Byproducts by TiO2 Photocatalyst Materials

by
Weijia Yu
1,
Marten in `t Veld
1,2,
Rossana Bossi
2,
Mohamed Ateia
3,4,
Dominique Tobler
1,
Anders Feilberg
5,
Nicolas Bovet
1 and
Matthew S. Johnson
1,*
1
Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen, Denmark
2
Department of Environmental Science, Aarhus University, Frederiksborgvej 399, DK-4000 Roskilde, Denmark
3
Department of Chemistry, Northwestern University, Evanston, IL 60208, USA
4
Department of Environmental Engineering and Earth Science, Clemson University, Clemson, SC 29634, USA
5
Department of Biological and Chemical Engineering, Aarhus University, Nordre Ringgade 1, DK-8000 Aarhus, Denmark
*
Author to whom correspondence should be addressed.
Sustainability 2021, 13(9), 4821; https://doi.org/10.3390/su13094821
Submission received: 30 March 2021 / Revised: 18 April 2021 / Accepted: 19 April 2021 / Published: 25 April 2021
(This article belongs to the Special Issue Sustainable Building and Sustainable Indoor Environment)
Browse Figures
Versions Notes

Abstract

:
Photocatalysts promised to control pollution in an environmentally benign manner, inexpensively, and with a low or cheap energy input. However, the limited chemical activity of photocatalysts has prevented their widespread use. This limitation has two important consequences; in addition to limited removal efficiency for pollution, photocatalysts may also generate unwanted byproducts due to incomplete reaction. This study focuses on the byproducts formed in the photocatalytic degradation of dimethyl sulfide (DMS) on titanium dioxide (TiO2), using a continuous flow reactor and detection via proton transfer reaction mass spectrometry. TiO2, activated carbon (AC), TiO2/AC (1:1) and TiO2/AC (1:5) were tested using either a laser-driven light source or LED lamps at 365 nm. The samples were characterized using a N2-BET surface area and pore size distributions, Scanning Electron Microscopy, X-ray Diffraction, and X-ray Photoelectron Spectroscopy, which confirmed that TiO2 was successfully coated on activated carbon without unexpected phases. TiO2 and activated carbon showed different removal mechanisms for DMS. The maximum yield of formaldehyde, 11.4%, was observed for DMS reacting on a TiO2/AC (1:5) composite operating at a DMS removal efficiency of 31.7% at 50 ∘ C. In addition to formaldehdye, significant products included acetone and dimethyl disulfide. In all, observed byproducts accounted for over half of the DMS material removed from the airstream. The TiO2/AC (1:5) and TiO2/AC (1:1) composites have a lower removal efficiency than TiO2, but a higher yield of byproducts. Experiments conducted from 20 ∘ C to 70 ∘ C showed that as temperature increases, the removal efficiency decreases and the production of byproducts increases even more. This is attributed both to decreased surface activity at high temperatures due to increased recombination of reactive species, and to the decreased residence time of volatile compounds on a hot surface. This study shows that potentially dangerous byproducts are formed by photocatalytic reactors because the reaction is incomplete under the conditions generally employed.

Graphical Abstract

1. Introduction

Air pollution is the leading environmental risk factor worldwide, killing an estimated 8.8 million people annually [1], rivaling tobacco smoke and exceeding deaths from all forms of violence combined [1,2]. Exposure to air pollutants increases the risk of respiratory and cardiovascular disease [3]. In addition, there are many associated negative impacts on society, including decreased performance and productivity [4], mental health issues [5], and an increase in violent crime [6]. Humans spend 80 to 90% of their time indoors, bringing increased attention to indoor air quality [7]. Photocatalysis is promoted as a solution to indoor air quality problems based on assertions regarding its low cost, energy efficiency, and environmentally benign character [8,9]. Photocatalytic oxidation has been studied for its ability to degrade many pollutants, including nitrogen oxides [10,11], sulfur dioxide [12,13], and volatile organic compounds (VOCs) [14,15,16], which are harmful to human health [3,17]. Photocatalysis could potentially find application in many devices, such as photocatalytic coatings and filters [4]. The efficiency of these materials is the subject of significant research and debate [15,18].
Many studies have been carried out on photocatalytic materials [19]. TiO2 has been studied the most frequently because it is cheap, non-toxic, biologically inert, and absorbs solar light [20,21,22]. The photocatalytic activity of TiO2 depends on its crystalline form. There are three main forms: anatase, rutile, and brookite [23,24]. Anatase is an indirect bandgap semiconductor and has been shown to have better photocatalytic properties than the other two phases, including a longer lifetime for its photoexcited electrons and holes [25]. Anatase can only be stimulated by light with a wavelength shorter than 400 nm [26], which limits its efficiency and applications. Rutile can be activated by visible light (bandgap 3.0 eV; absorbs wavelengths around 400 nm) [27], but because of the rapid recombination of electrons and holes [28], it is not able to maintain a high surface activity as a photocatalyst. Degussa P25 is a photocatalyst composed of anatase and rutile (the reported ratio being typically 70:30 or 80:20) [29,30,31] which is widely used due to its relatively high photocatalytic activity [32].
Activated carbon (AC) is commonly used for pollution control and works through a mechanism of adsorption rather than photocatalytic degradation. It is inexpensive, stable, and durable, with a large specific surface area and pore volume. The combination of TiO2 with activated carbon has been studied since the 90s [33,34,35,36,37,38]. These studies show that the combination of TiO2 and AC has a higher photocatalytic efficiency than either pure activated carbon or pure TiO2 [39,40,41] and improved removal efficiency compared to TiO2 alone in a high-humidity environment ([42]). Carbon-doped TiO2 has been shown to respond to visible light, and has higher removal efficiency than undoped TiO2 [43,44]. Activated carbon may improve TiO2 photocatalytic degradation by concentrating the pollutants and intermediates for reaction with TiO2. The pollutants stored in AC can then be destroyed by TiO2, leading to the regeneration of AC. Finally, the presence of AC limits the coagulation of TiO2, thus improving its photocatalytic efficiency.
While it is often claimed that by using photocatalysts, VOC pollution will be completely degraded into CO2 and H2O [15], this assertion is incomplete and inaccurate. The surface activity of a photocatalyst is self-limiting due to recombination reactions. Only a certain activity can be maintained. An additional concern is that volatile compounds, including volatile reaction products, spend little time on the surface, decreasing the probability of reaction and increasing treatment time. Most studies investigating photocatalytic removal of VOCs calculate the removal efficiency [45,46,47], or compare the CO2 production [48,49,50] of different materials [47,51,52]. For one thing, the treatment times, space velocities, and energy used in these studies are often not practical for applications in the real world. For another, few groups report the yield of CO2 and H2O relative to the amount of pollutant consumed. Moreover, monitoring many byproducts including formaldehyde and multiply-oxygenated species requires special techniques that are not always available [53]. A full picture can only be given by considering the mass or atom budgets that describe how much reagent has been lost and which products have been formed, including byproducts.
Although there are studies indicating that photocatalytic oxidation does not completely oxidize organics to CO2 and H2O, only a few have examined the byproducts. Selishchev et al. [54] found CO was formed along with CO2 and H2O during photocatalytic oxidation of VOCs. Mo et al. [49] found that humidity and VOC concentration affected the formation and concentration of byproducts in a study of the degradation of toluene. Yao and Feilberg observed the formation of methane thiol and S-methyl-methanethiosulfonate from sulfur-containing precursors [55]. Wang and coworkers studied the degradation of DMS on TiO2, characterizing the products using chromatography, and did not report CH2O concentrations [56]. Lin et al. saw formaldehyde production from S-doped TiO2 photocatalysts but did not report the yield [57]. Although photocatalysts are studied in the context of indoor air quality, it is essential to characterize byproduct formation in order to conclude that photocatalytic devices are safe and effective. More studies are clearly needed that quantify the yields of CO2 and H2O in relation to the loss of precusors, and that account for the transfer of material into byproducts.
In some cases, such as the decomposition of a hydrocarbon-yielding formaldehyde, the products are more dangerous than the original pollutant. Formaldehyde is toxic to humans and animals in small quantities [58]. In 2010, the World Health Organization (WHO) established an indoor air quality guideline for short- and long-term exposure to formaldehyde of 0.1 mg/m 3 (0.08 ppm) for all 30 min periods [59]. The German Federal Agency of Health set a maximum formaldehyde mixing ratio of 0.1 ppm for indoor air, and the US National Institute for Occupational Safety and Health (NIOSH) set a time-weighted average concentration exposure limit for a 10 h workday during a 40 h workweek for formaldehyde of 0.016 ppm [60].
Reduced sulfur compounds are associated with strong odor discomfort and are often a serious pollution problem [61]. They are produced by many processes, such as cooking cabbage, beet, or seafood, by bacteria, and in wastewater treatment. DMS with a very low odor threshold of 0.6–30 ppb [62] is the most abundant biological sulfur compound emitted to the atmosphere. Although its main atmospheric source is marine phytoplankton [63], it is produced by many processes, such as those listed here, and is commonly found in indoor environments. For example, DMS produced by livestock can be the cause of tension between livestock producers and nearby residents. The literature shows that indoor concentrations of DMS are highly variable, ranging from ppt to tens or hundreds of ppb [64,65].
Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) is a powerful method for monitoring byproducts at ppbv levels in real-time that is able to overcome the limited sampling frequency of methods such as gas chromatography-mass spectrometry (GC-MS) [66]. In this work, online PRT-MS was used to monitor the concentrations of DMS and other volatile byproducts.
This study was carried out in order to better characterize the formation of byproducts by common photocatalysts. In particular, we focused on the degradation and byproducts from dimethyl sulfide, important in its own right and as a representative of odorous sulfur compounds in general. Here, we describe the activity, reaction mechanisms, extent of reaction, and yields of several volatile byproducts under typical photocatalyst operating conditions for TiO2 and composite TiO2-activated carbon materials, using PTR-MS for accurate and wide-ranging characterisation of reaction products.

2. Results And Discussion

2.1. Characterization

The success of the synthesis and the ratio of the TiO2/AC was confirmed using SEM, the BET adsorption isotherm method, XPS, and XRD. The details can be found in the electronic Supplementary Materials. Characterizations confirm the successful synthesis of TiO2/AC (1:1) and TiO2/AC (1:5), see Supplementary Materials.

2.2. Byproducts

Figure 1 shows the PTR-MS photocatalysis response for experiments testing the TiO2 photocatalytic removal of DMS. Mass to charge ratios (m/z) of 31, 46, 59, 63, and 95 were detected by PTR-MS in full scan mode, assigned to formaldehyde, acetone, formic acid, DMS, and dimethyl disulfide (DMDS), respectively [55]. Those products are probable byproducts of DMS breakdown by · OH and h + [67]. When irradiated with the LDLS lamp, the DMS concentration rapidly decreased by approximately 47.4% and the concentrations of formaldehyde and acetone increased by ca. 20 and 5 ppb, respectively. A minor amount of formic acid was present as an impurity in the gasline, and can be seen in Figure 1. When the lamp was turned on, its concentration also decreased by about 46%. When the LDLS was turned off, the concentrations of DMS and formic acid increased again, while the concentrations of formaldehyde and acetone showed a clear decrease, which indicates that those products are generated by the photocatalytic process. Blank tests were performed under the following conditions: (1) Blank filter with DMS and LDLS light irradiation, and (2) TiO2 coated filter with LDLS light irradiation. No byproducts were detected in the blank test.
As shown in Figure 1, during the photocatalytic degradation, the yields of formaldehyde, acetone, DMDS are 5.2%, 1.8% and −0.5%; similar values have been reported in other work, formaldehyde was reported as a byproduct of photocatalytic oxidation of toluene [55,64]. Soni and coworkers have investigated the degradation of DMS on oxidising metal oxide catalyst surfaces and theorize that nucleophilic lattice-stablized M − O − is responsible for the formation of partial oxidation products [68].
Figure 2 shows the DMS photocatalytic removal efficiency for TiO2/AC (1:1) photocatalyst excited with the LDLS lamp including DMS byproducts. As shown in Figure 2, the reaction process goes through two phases. Initially, concentrations decrease without byproduct formation, attributed to adsorption on AC. After the AC is saturated, indicated by the return to initial/baseline concentration, the LDLS is turned on and we attribute product formation to TiO2 photocatalysis. The concentration of DMS decreases by 23%. The decrease in DMS is less than that for pure TiO2. For this phase, the yields of formaldehyde, acetone, and DMDS are 12.3%, 0.5%, and −0.2%, respectively.
Figure 3 shows the photocatalytic degradation of DMS on TiO2/AC (1:5) with the LDLS lamp, including byproducts. The behavior is similar as for TiO2/AC (1:1), though with a longer breakthrough time. The removal efficiency of DMS was 13.4% on TiO2/AC (1:5). The yields χ of formaldehyde and acetone are 11.2% and 2.4%, respectively, and other intermediates are below the detection limit.
The removal efficiency of DMS and byproduct yield χ are summarized in Table 1. The removal of DMS decreases with a decrease in a TiO2 mixing ratio in substrates. The adsorption capacity q e is reported as a mass fraction of adsorbed gas to filter mass [69].
The q e of TiO2/AC (1:1) and TiO2/AC (1:5) are found to be 43.9 mg/g and 46.9 mg/g; the adsorption capacity increases with increasing AC. While the lower TiO2 loading showed lower removal of DMS, it showed a relatively higher yield of byproducts (Table 1).
A scheme for the reactions of organosulfur compounds on TiO2 is presented in Figure 4 [70,71]; the mechanism of acetone formation is unclear.

2.3. Influence of Temperature

TiO2 and AC/TiO2 (1:1) were chosen for a study of the effect of temperature on catalytic performance and byproduct formation. Conditions were 20 ∘ C, 30 ∘ C, 50 ∘ C, and 70 ∘ C, using the LDLS lamp as the light source.
Figure 5 shows the removal efficiency and byproduct formation for DMS degradation at different temperatures on TiO2. The concentrations of DMS and DMDS increase with temperature, which can be related to desorption. As summarized in Table 2, when the temperature is elevated from 20 to 70 ∘ C, the RE of DMS decreases from 58.1% to 48.1% and byproduct yield decreases. The highest yield of byproducts is observed at 50 ∘ C with 21.0% for formaldehyde and 15.5% for acetone. In contrast to larger molecules, small molecules spend less time on the surface, and therefore have a lower probability of reaction. Table 3 summarises some key physical properties of these small molecules. Formaldehyde has the lowest vapor pressure, giving less time on the photocatalyst surface. This, combined with a mechanism favoring its production, means that it is one of the most abundant byproducts.
Figure 6 and Table 4 show the removal efficiency and byproduct formation for the degradation DMS on TiO2/AC (1:1) from 20 to 70 °C. The temperature has a great impact on byproduct formation by TiO2/AC (1:1) by affecting both the residence time of molecules on the surface and the recombination rate of radicals. Overall, the DMS removal efficiency decreased. Values were 28.2, 32.9, 16, and 11.1% at 20, 30, 50, and 70 ∘ C, respectively. The yield of byproducts was at a maximum of 50 ∘ C with formaldehyde, acetone, and DMDS yields of 32.7%, 21.2%, and 1.0%, respectively. Unlike TiO2, byproduct generation did not decrease with f for TiO2/AC (1:1). At 70 ∘ C the yield of formaldehyde decreased to 20.4%. It is worth noting that there is a significant decrease of byproduct yield at 70 ∘ C in both TiO2 and TiO2/AC (1:1) experiments. Compared to TiO2, TiO2/AC (1:1) has lower f D M S and χ at all temperatures. The results are consistent with a mechanism whereby surface activity decreases at higher temperatures, and in addition, the residence time of volatile byproducts on the surface decreases more rapidly than it does for DMS. The overall effect is decreased pollution removal and more formation of byproducts as temperature increases.

3. Materials And Methods

3.1. Materials

TiO2 P25 was purchased from Sigma Aldrich, Steinheim, Germany, and AC was purchased from Cica-Reagent, Kanto Chemical Co., Inc., Tokyo, Japan. The TiO2-AC powders were synthesized by sonicating AC for 1 min in 50 mL of ethanol for each carbonaceous material (solution A). The TiO2 powder was sonicated in 50 mL of ethanol for 1 min (solution B). Thereafter, solution A and solution B were mixed with mass ratios 1:5 and 1:1, and sonicated for 1 min, followed by mixing for 12 h to produce solution C. After the mixing, solution C was filtered through a vacuum filter machine equipped with a fiberglass filter to separate the product from the supernatant. Afterward, the filter was dried at room temperature for 24 h.

3.2. Methods

The photocatalytic activity of the samples towards dimethyl sulfide (DMS) (Sigma-Aldrich, ≥99%, Steinheim, Germany) under the irradiation of simulated solar light was measured in a continuous flow stainless-steel gas-phase reactor with a quartz window. Samples were irradiated using either a Laser-Driven Light-Source (LDLS, ENERGETIC, 140 W, EQ-99, Wilmington, NC, USA) in combination with a bandpass filter, or with UV light emitting diodes (LED). The LDLS has a spectral distribution similar to the sun. A long-pass filter (335 nm wavelength, Jenaer Glaswerk Schott & Gen., Mainz, Germany) was used to limit irradiation to the region from 335 nm to 2000 nm. Four LED lamps (365–370 nm, 3 W, Hotred, China) were used.
TiO2, AC, and TiO2/AC powders were coated on quartz fiber filters (diameter: 47 mm, Whatman, Germany), and the filter was placed in the middle of the reactor (inner diameter: 40 mm, height: 40 mm, cylinder with quartz window). The flow enters from the top of the filter, then leaves from the bottom.
Dry air from a technical air supply was branched into two. One stream flowed through a bubbler with DMS in squalene and the flow from the other adjusted to further control the DMS mixing ratio (Figure 7). The flow rates of the DMS bubbler and the dilution line were controlled by mass flow controllers (Model 0254, Brooks Instruments, Hatfield, PA, USA). The two branch lines were merged at the reactor. The initial concentrations of DMS in the air varied between 300 and 600 ppb. DMS concentrations in the outlet gas mixtures were monitored using PTR-MS (PTR-ToF 8000, Ionicon Analytik GmbH, Innsbruck, Austria). The composition was recorded every second throughout a photolysis experiment. Before irradiation, the air stream with a known concentration of DMS was allowed to flow through the bypass. After the concentrations stabilised, the flow was changed from bypass to reactor until the equilibrium "dark" adsorption of DMS on the samples was established. When the DMS concentrations leaving the reactor were stabilized and equivalent to the concentration before the bypass, the equilibrium was considered to have been reached, and samples would be irradiated by light until the concentration was stable. The removal efficiency f of DMS is given by:
f = C i n − C o u t C i n ,
where C i n and C o u t are the concentrations measured at the inlet and outlet of the reactor, respectively. The yield of byproducts χ is defined as:
χ = Δ C o u t Δ C i n .

3.3. Characterization

Surface topography was characterised using Scanning Electron Microscopy (SEM, FEI Quanta 3D). The crystal phase and structure of samples were analyzed by X-ray Diffraction (XRD, Bruker D8 Advance Da Vinci). Surface area, total pore volume, and average pore size were analyzed using the BET adsorption isotherm method on a Quantachrome, Autosorb-1. XPS was used to characterize the differences in surface composition. A Kratos AXIS ULTRADLD XPS was used for measurement, and the CasaXPS software was used for data processing. The concentration of gases (in ppbv) was measured by PTR-MS. The PTR-MS samples air continuously into the drift tube where the sample collides with the primary ion H3O+, ionizing the compounds via gas phase proton transfer. The proton affinity of water is 691 kJ mol − 1 , and only compounds with proton affinities above 691 kJ mol − 1 can be detected by PTR-MS [55].

3.4. Formaldehyde Calibration

The proton affinity of formaldehyde (712.9 kJ/mol) is only 22 kJ/mol higher than the proton affinity of water. Therefore, the formaldehyde signal depends on the humidity [72]), in contrast to most other species detected with PTRMS [73,74,75,76]. A formaldehyde calibration based on two parameters (the formaldehyde sensitivity and the humidity) was performed, arriving at the values we have reported. As a formaldehyde permeation system was not available, the formaldehyde sensitivity was determined using the method of Wisthaler et al. [77]. In this method, acetaldehyde was used as a surrogate for formaldehyde. Acetaldehyde is a useful surrogate as its chemical and physical properties closely resemble formaldehyde. In their research, Wisthaler et al. calculated that this method added an additional uncertainty of 10% compared to a formaldehyde calibration. Using two different calibration gases, the acetaldehyde (and the formaldehyde) sensitivity of the PTR-MS was set at 101.38667 ± 0.036% ccps/ppb. With the sensitivity known, the impact of the humidity on the formaldehyde concentrations could be determined. The humidity correction factor (HCF) was calculated by measuring concentrations of formaldehyde in an environmental chamber simultaneously with a PTR-MS and dinitrophenylhydrazine (DNPH) cartridges, which are not affected by humidity [77,78]. The cartridges were analysed using high-performance liquid chromatography with ultraviolet spectroscopy (HPLC-UV). Four measurements were performed in the relative humidity range of 30 to 65%, which showed a linear relationship between the methods [79]:
H C F = 0.257 ∗ A H + 3.6722 ,
where AH is the absolute humidity in gm − 3 . Finally, the formaldehyde concentrations were determined using the following formula:
H C H O p p b = H C H O c c p s 101.38667 ∗ ( 0.257 ∗ A H + 3.6722 ) ,
where HCHO p p b is the formaldehyde concentration in the ppb level, and HCHO c c p s is the signal of formaldehyde in corrected counts per second.

4. Conclusions

TiO2, TiO2/AC (1:1), and TiO2/AC (1:5) samples were tested for DMS removal. While under LDLS irradiation, the main byproducts generated by TiO2 were formaldehyde and acetone. The byproduct yield increased with TiO2 loading. For TiO2, DMS removal efficiency decreased, and byproduct yield increased as a function of temperature. TiO2/AC (1:1) performed differently than TiO2 since AC is able to release stored pollutants with increasing temperature. At a higher temperature, the f D M S of TiO2/AC (1:1) decreased, and the byproduct yield increased. The most common byproduct is formaldehyde, which reached a maximum yield of 31.7% at 50 ∘ C on TiO2/AC (1:1) substrate. We conclude that surface activity decreases at a higher temperature due to increased loss of radicals to recombination reactions, and in addition, the residence time of volatile byproducts on the surface decreases more rapidly than it does for DMS. The overall effect is decreased pollution removal and more formation of byproducts as temperature increases. None of the substrates was capable of fully degrading DMS into CO2 and H2O under the conditions of the study. At higher temperatures, both DMS and intermediates spend less time on the surface, limiting their removal; at the same time, surface activity drops as temperature increases due to increased loss of radicals. In conclusion, care must be taken to include consideration of byproduct formation when evaluating the performance of photocatalysts, particularly for indoor applications where there is potential for accumulation of toxic products.

Supplementary Materials

The following are available at https://www.mdpi.com/article/10.3390/su13094821/s1.

Author Contributions

Conceptualization, W.Y. and M.S.J.; Methodology, W.Y. and M.S.J.; Software, M.i.`tV., D.T.; Validation, W.Y. and M.S.J.; Formal analysis, W.Y. and M.S.J.; Investigation, W.Y., M.i.`tV.; Resources, D.T., R.B., A.F., M.A. and N.B.; Data curation, W.Y.; Writing—original draft preparation, W.Y.; Writing—review and editing, M.S.J.; Visualization, W.Y.; Supervision, M.S.J.; Project administration, M.S.J.; Funding acquisition, W.Y. and M.S.J. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Chinese Scholarship Council and University of Copenhagen, Department of Chemistry.

Data Availability Statement

The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy.

Acknowledgments

We would like to thank Dion Awfa for proving some of the materials used in the experiments and Henning Osholm Sørensen for technical support with XRD.

Conflicts of Interest

MSJ is employed by the University of Copenhagen and by Airlabs, a company specialising in air pollution detection and control.

References

  1. Lelieveld, J.; Pozzer, A.; Pöschl, U.; Fnais, M.; Haines, A.; Münzel, T. Loss of life expectancy from air pollution compared to other risk factors: A worldwide perspective. Cardiovasc. Res. 2020, 116, 1910–1917. [Google Scholar] [CrossRef]
  2. Landrigan, P.J.; Fuller, R.; Acosta, N.J.; Adeyi, O.; Arnold, R.; Baldé, A.B.; Bertollini, R.; Bose-O’Reilly, S.; Boufford, J.I.; Breysse, P.N.; et al. The Lancet Commission on pollution and health. Lancet 2018, 391, 462–512. [Google Scholar] [CrossRef] [Green Version]
  3. Brunekreef, B.; Holgate, S.T. Air pollution and health. Lancet 2002, 360, 1233–1242. [Google Scholar] [CrossRef]
  4. Wyon, D.P. The effects of indoor air quality on performance and productivity. Indoor Air 2004, 14, 92–101. [Google Scholar] [CrossRef] [PubMed]
  5. Chen, S.; Oliva, P.; Zhang, P. Air Pollution and Mental Health: Evidence from China; Technical Report; National Bureau of Economic Research: Cambridge, MA, USA, 2018. [Google Scholar]
  6. Burkhardt, J.; Bayham, J.; Wilson, A.; Berman, J.D.; O’Dell, K.; Ford, B.; Fischer, E.V.; Pierce, J.R. The relationship between monthly air pollution and violent crime across the United States. J. Environ. Econ. Policy 2020, 9, 188–205. [Google Scholar] [CrossRef]
  7. Saini, J.; Dutta, M.; Marques, G. A comprehensive review on indoor air quality monitoring systems for enhanced public health. Sustain. Environ. Res. 2020, 30, 6. [Google Scholar] [CrossRef] [Green Version]
  8. Beeldens, A. An environmental friendly solution for air purification and self-cleaning effect: The application of TiO2 as photocatalyst in concrete. In Proceedings of the Transport Research Arena Europe—TRA, Göteborg, Sweden, 12–15 June 2006; pp. 12–16. [Google Scholar]
  9. Asahi, R.; Morikawa, T.; Ohwaki, T.; Aoki, K.; Taga, Y. Visible-light photocatalysis in nitrogen-doped titanium oxides. Science 2001, 293, 269–271. [Google Scholar] [CrossRef] [PubMed]
  10. Maggos, T.; Bartzis, J.; Liakou, M.; Gobin, C. Photocatalytic degradation of NOx gases using TiO2-containing paint: A real scale study. J. Hazard. Mater. 2007, 146, 668–673. [Google Scholar] [CrossRef] [PubMed]
  11. Maggos, T.; Plassais, A.; Bartzis, J.; Vasilakos, C.; Moussiopoulos, N.; Bonafous, L. Photocatalytic degradation of NOx in a pilot street canyon configuration using TiO2-mortar panels. Environ. Monit. Assess. 2008, 136, 35–44. [Google Scholar] [CrossRef]
  12. Yuan, Y.; Zhang, J.; Li, H.; Li, Y.; Zhao, Y.; Zheng, C. Simultaneous removal of SO2, NO and mercury using TiO2-aluminum silicate fiber by photocatalysis. Chem. Eng. J. 2012, 192, 21–28. [Google Scholar] [CrossRef]
  13. Liu, H.; Yu, X.; Yang, H. The integrated photocatalytic removal of SO2 and NO using Cu doped titanium dioxide supported by multi-walled carbon nanotubes. Chem. Eng. J. 2014, 243, 465–472. [Google Scholar] [CrossRef]
  14. Alberici, R.M.; Jardim, W.F. Photocatalytic destruction of VOCs in the gas-phase using titanium dioxide. Appl. Catal. B Environ. 1997, 14, 55–68. [Google Scholar] [CrossRef]
  15. Mo, J.; Zhang, Y.; Xu, Q.; Lamson, J.J.; Zhao, R. Photocatalytic purification of volatile organic compounds in indoor air: A literature review. Atmos. Environ. 2009, 43, 2229–2246. [Google Scholar] [CrossRef]
  16. Kim, S.B.; Hong, S.C. Kinetic study for photocatalytic degradation of volatile organic compounds in air using thin film TiO2 photocatalyst. Appl. Catal. B Environ. 2002, 35, 305–315. [Google Scholar] [CrossRef]
  17. Xu, T.; Zheng, H.; Zhang, P. Performance of an innovative VUV-PCO purifier with nanoporous TiO2 film for simultaneous elimination of VOCs and by-product ozone in indoor air. Build. Environ. 2018, 142, 379–387. [Google Scholar] [CrossRef]
  18. Ren, H.; Koshy, P.; Chen, W.F.; Qi, S.; Sorrell, C.C. Photocatalytic materials and technologies for air purification. J. Hazard. Mater. 2017, 325, 340–366. [Google Scholar] [CrossRef]
  19. Di Paola, A.; García-López, E.; Marcì, G.; Palmisano, L. A survey of photocatalytic materials for environmental remediation. J. Hazard. Mater. 2012, 211, 3–29. [Google Scholar] [CrossRef] [PubMed]
  20. Palanisamy, B.; Babu, C.; Sundaravel, B.; Anandan, S.; Murugesan, V. Sol–gel synthesis of mesoporous mixed Fe2O3/TiO2 photocatalyst: Application for degradation of 4-chlorophenol. J. Hazard. Mater. 2013, 252, 233–242. [Google Scholar] [CrossRef] [PubMed]
  21. Fujishima, A.; Honda, K. Electrochemical photolysis of water at a semiconductor electrode. Nature 1972, 238, 37–38. [Google Scholar] [CrossRef]
  22. Linsebigler, A.L.; Lu, G.; Yates, J.T., Jr. Photocatalysis on TiO2 surfaces: Principles, mechanisms, and selected results. Chem. Rev. 1995, 95, 735–758. [Google Scholar] [CrossRef]
  23. Xu, M.; Shao, S.; Gao, B.; Lv, J.; Li, Q.; Wang, Y.; Wang, H.; Zhang, L.; Ma, Y. Anatase (101)-like structural model revealed for metastable rutile TiO2 (011) surface. ACS Appl. Mater. Interfaces 2017, 9, 7891–7896. [Google Scholar] [CrossRef] [PubMed]
  24. Yu, J.; Yu, H.; Cheng, B.; Zhou, M.; Zhao, X. Enhanced photocatalytic activity of TiO2 powder (P25) by hydrothermal treatment. J. Mol. Catal. A Chem. 2006, 253, 112–118. [Google Scholar] [CrossRef]
  25. Zhang, X.; Zhou, M.; Lei, L. TiO2 photocatalyst deposition by MOCVD on activated carbon. Carbon 2006, 44, 325–333. [Google Scholar] [CrossRef]
  26. Sun, Q.; Lv, K.; Zhang, Z.; Li, M.; Li, B.; others. Effect of contact interface between TiO2 and g-C3N4 on the photoreactivity of g-C3N4/TiO2 photocatalyst: (0 0 1) vs. (1 0 1) facets of TiO2. Appl. Catal. B Environ. 2015, 164, 420–427. [Google Scholar]
  27. Ohno, T.; Tsubota, T.; Toyofuku, M.; Inaba, R. Photocatalytic activity of a TiO2 photocatalyst doped with C4+ and S 4+ ions having a rutile phase under visible light. Catal. Lett. 2004, 98, 255–258. [Google Scholar] [CrossRef] [Green Version]
  28. Zhang, J.; Zhou, P.; Liu, J.; Yu, J. New understanding of the difference of photocatalytic activity among anatase, rutile and brookite TiO2. Phys. Chem. Chem. Phys. 2014, 16, 20382–20386. [Google Scholar] [CrossRef]
  29. Ohtani, B.; Prieto-Mahaney, O.; Li, D.; Abe, R. What is Degussa (Evonik) P25? Crystalline composition analysis, reconstruction from isolated pure particles and photocatalytic activity test. J. Photochem. Photobiol. A Chem. 2010, 216, 179–182. [Google Scholar] [CrossRef] [Green Version]
  30. Hurum, D.C.; Agrios, A.G.; Gray, K.A.; Rajh, T.; Thurnauer, M.C. Explaining the enhanced photocatalytic activity of Degussa P25 mixed-phase TiO2 using EPR. J. Phys. Chem. B 2003, 107, 4545–4549. [Google Scholar] [CrossRef]
  31. Ohno, T.; Sarukawa, K.; Tokieda, K.; Matsumura, M. Morphology of a TiO2 photocatalyst (Degussa, P-25) consisting of anatase and rutile crystalline phases. J. Catal. 2001, 203, 82–86. [Google Scholar] [CrossRef]
  32. Quesada-Cabrera, R.; Mills, A.; O’Rourke, C. Action spectra of P25 TiO2 and a visible light absorbing, carbon-modified titania in the photocatalytic degradation of stearic acid. Appl. Catal. B Environ. 2014, 150, 338–344. [Google Scholar] [CrossRef]
  33. Torimoto, T.; Okawa, Y.; Takeda, N.; Yoneyama, H. Effect of activated carbon content in TiO2-loaded activated carbon on photodegradation behaviors of dichloromethane. J. Photochem. Photobiol. A Chem. 1997, 103, 153–157. [Google Scholar] [CrossRef]
  34. Heu, R.; Ateia, M.; Awfa, D.; Punyapalakul, P.; Yoshimura, C. Photocatalytic Degradation of Organic Micropollutants in Water by Zr-MOF/GO Composites. J. Compos. Sci. 2020, 4, 54. [Google Scholar] [CrossRef]
  35. Ateia, M.; Alalm, M.G.; Awfa, D.; Johnson, M.S.; Yoshimura, C. Modeling the degradation and disinfection of water pollutants by photocatalysts and composites: A critical review. Sci. Total Environ. 2020, 698, 134197. [Google Scholar] [CrossRef]
  36. Awfa, D.; Ateia, M.; Fujii, M.; Johnson, M.S.; Yoshimura, C. Photodegradation of pharmaceuticals and personal care products in water treatment using carbonaceous-TiO2 composites: A critical review of recent literature. Water Res. 2018, 142, 26–45. [Google Scholar] [CrossRef]
  37. Awfa, D.; Ateia, M.; Fujii, M.; Yoshimura, C. Novel magnetic carbon nanotube-TiO2 composites for solar light photocatalytic degradation of pharmaceuticals in the presence of natural organic matter. J. Water Process. Eng. 2019, 31, 100836. [Google Scholar] [CrossRef]
  38. Shimizu, Y.; Ateia, M.; Wang, M.; Awfa, D.; Yoshimura, C. Disinfection mechanism of E. coli by CNT-TiO2 composites: Photocatalytic inactivation vs. physical separation. Chemosphere 2019, 235, 1041–1049. [Google Scholar] [CrossRef] [PubMed]
  39. Takeda, N.; Iwata, N.; Torimoto, T.; Yoneyama, H. Influence of carbon black as an adsorbent used in TiO2 photocatalyst films on photodegradation behaviors of propyzamide. J. Catal. 1998, 177, 240–246. [Google Scholar] [CrossRef]
  40. Ibusuki, T.; Takeuchi, K. Removal of low concentration nitrogen oxides through photoassisted heterogeneous catalysis. J. Mol. Catal. 1994, 88, 93–102. [Google Scholar] [CrossRef]
  41. Xu, Y.; Langford, C.H. Photoactivity of titanium dioxide supported on MCM41, zeolite X, and zeolite Y. J. Phys. Chem. B 1997, 101, 3115–3121. [Google Scholar] [CrossRef]
  42. Ao, C.; Lee, S. Combination effect of activated carbon with TiO2 for the photodegradation of binary pollutants at typical indoor air level. J. Photochem. Photobiol. A Chem. 2004, 161, 131–140. [Google Scholar] [CrossRef]
  43. Irie, H.; Watanabe, Y.; Hashimoto, K. Carbon-doped anatase TiO2 powders as a visible-light sensitive photocatalyst. Chem. Lett. 2003, 32, 772–773. [Google Scholar] [CrossRef]
  44. Chatterjee, A.; Wu, S.B.; Chou, P.W.; Wong, M.; Cheng, C.L. Observation of carbon-facilitated phase transformation of titanium dioxide forming mixed-phase titania by confocal Raman microscopy. J. Raman Spectrosc. 2011, 42, 1075–1080. [Google Scholar] [CrossRef]
  45. Fang, J.; Chen, Z.; Zheng, Q.; Li, D. Photocatalytic decomposition of benzene enhanced by the heating effect of light: Improving solar energy utilization with photothermocatalytic synergy. Catal. Sci. Technol. 2017, 7, 3303–3311. [Google Scholar] [CrossRef]
  46. Wang, L.; Zhang, Y.; Gu, X.; Zhang, Y.; Su, H. Insight into the role of UV-irradiation in photothermal catalytic Fischer–Tropsch synthesis over TiO2 nanotube-supported cobalt nanoparticles. Catal. Sci. Technol. 2018, 8, 601–610. [Google Scholar] [CrossRef]
  47. Zeng, M.; Li, Y.; Mao, M.; Bai, J.; Ren, L.; Zhao, X. Synergetic effect between photocatalysis on TiO2 and thermocatalysis on CeO2 for gas-phase oxidation of benzene on TiO2/CeO2 nanocomposites. ACS Catal. 2015, 5, 3278–3286. [Google Scholar] [CrossRef]
  48. Lan, L.; Li, Y.; Zeng, M.; Mao, M.; Ren, L.; Yang, Y.; Liu, H.; Yun, L.; Zhao, X. Efficient UV–vis-infrared light-driven catalytic abatement of benzene on amorphous manganese oxide supported on anatase TiO2 nanosheet with dominant {001} facets promoted by a photothermocatalytic synergetic effect. Appl. Catal. B Environ. 2017, 203, 494–504. [Google Scholar] [CrossRef]
  49. Zheng, Y.; Wang, W.; Jiang, D.; Zhang, L. Amorphous MnOx modified Co3O4 for formaldehyde oxidation: Improved low-tempe rature catalytic and photothermocatalytic activity. Chem. Eng. J. 2016, 284, 21–27. [Google Scholar] [CrossRef]
  50. Chen, J.; Li, Y.; Fang, S.; Yang, Y.; Zhao, X. UV–Vis-infrared light-driven thermocatalytic abatement of benzene on Fe doped OMS-2 nanorods enhanced by a novel photoactivation. Chem. Eng. J. 2018, 332, 205–215. [Google Scholar] [CrossRef]
  51. Ji, J.; Xu, Y.; Huang, H.; He, M.; Liu, S.; Liu, G.; Xie, R.; Feng, Q.; Shu, Y.; Zhan, Y.; et al. Mesoporous TiO2 under VUV irradiation: Enhanced photocatalytic oxidation for VOCs degradation at room temperature. Chem. Eng. J. 2017, 327, 490–499. [Google Scholar] [CrossRef]
  52. Fang, S.; Li, Y.; Yang, Y.; Chen, J.; Liu, H.; Zhao, X. Mg-doped OMS-2 nanorods: A highly efficient catalyst for purification of volatile organic compounds with full solar spectrum irradiation. Environ. Sci. Nano 2017, 4, 1798–1807. [Google Scholar] [CrossRef]
  53. Russell, H.S.; Bonomaully, J.; Bossi, R.; Hofmann, M.E.; Knap, H.C.; Pernov, J.B.; Veld, M.; Johnson, M.S. Novel Materials for Combined Nitrogen Dioxide and Formaldehyde Pollution Control under Ambient Conditions. Catalysts 2020, 10, 1040. [Google Scholar] [CrossRef]
  54. Selishchev, D.; Kolobov, N.; Pershin, A.; Kozlov, D. TiO2 mediated photocatalytic oxidation of volatile organic compounds: Formation of CO as a harmful by-product. Appl. Catal. B Environ. 2017, 200, 503–513. [Google Scholar] [CrossRef]
  55. Yao, H.; Feilberg, A. Characterisation of photocatalytic degradation of odorous compounds associated with livestock facilities by means of PTR-MS. Chem. Eng. J. 2015, 277, 341–351. [Google Scholar] [CrossRef]
  56. Wang, Z.; Liu, J.; Dai, Y.; Dong, W.; Zhang, S.; Chen, J. Dimethyl sulfide photocatalytic degradation in a light-emitting-diode continuous reactor: Kinetic and mechanistic study. Ind. Eng. Chem. Res. 2011, 50, 7977–7984. [Google Scholar] [CrossRef]
  57. Lin, Y.H.; Hsueh, H.T.; Chang, C.W.; Chu, H. The visible light-driven photodegradation of dimethyl sulfide on S-doped TiO2: Characterization, kinetics, and reaction pathways. Appl. Catal. B Environ. 2016, 199, 1–10. [Google Scholar] [CrossRef]
  58. Li, Y.; Chen, N.; Deng, D.; Xing, X.; Xiao, X.; Wang, Y. Formaldehyde detection: SnO2 microspheres for formaldehyde gas sensor with high sensitivity, fast response/recovery and good selectivity. Sens. Actuators B Chem. 2017, 238, 264–273. [Google Scholar] [CrossRef]
  59. Nielsen, G.D.; Larsen, S.T.; Wolkoff, P. Re-evaluation of the WHO (2010) formaldehyde indoor air quality guideline for cancer risk assessment. Arch. Toxicol. 2017, 91, 35–61. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  60. Nie, L.; Yu, J.; Jaroniec, M.; Tao, F.F. Room-temperature catalytic oxidation of formaldehyde on catalysts. Catal. Sci. Technol. 2016, 6, 3649–3669. [Google Scholar] [CrossRef]
  61. Cho, K.S.; Hirai, M.; Shoda, M. Degradation characteristics of hydrogen sulfide, methanethiol, dimethyl sulfide and dimethyl disulfide by Thiobacillus thioparus DW44 isolated from peat biofilter. J. Ferment. Bioeng. 1991, 71, 384–389. [Google Scholar] [CrossRef]
  62. De Zwart, J.M.; Kuenen, J.G. C 1-cycle of sulfur compounds. Biodegradation 1992, 3, 37–59. [Google Scholar] [CrossRef]
  63. Charlson, R.J.; Lovelock, J.E.; Andreae, M.O.; Warren, S.G. Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate. Nature 1987, 326, 655–661. [Google Scholar] [CrossRef]
  64. Zhao, W.; Dai, J.; Liu, F.; Bao, J.; Wang, Y.; Yang, Y.; Yang, Y.; Zhao, D. Photocatalytic oxidation of indoor toluene: Process risk analysis and influence of relative humidity, photocatalysts, and VUV irradiation. Sci. Total Environ. 2012, 438, 201–209. [Google Scholar] [CrossRef]
  65. Vildozo, D.; Portela, R.; Ferronato, C.; Chovelon, J.M. Photocatalytic oxidation of 2-propanol/toluene binary mixtures at indoor air concentration levels. Appl. Catal. B Environ. 2011, 107, 347–354. [Google Scholar] [CrossRef]
  66. Irokawa, Y.; Morikawa, T.; Aoki, K.; Kosaka, S.; Ohwaki, T.; Taga, Y. Photodegradation of toluene over TiO2- X N X under visible light irradiation. Phys. Chem. Chem. Phys. 2006, 8, 1116–1121. [Google Scholar] [CrossRef] [PubMed]
  67. Cantau, C.; Larribau, S.; Pigot, T.; Simon, M.; Maurette, M.; Lacombe, S. Oxidation of nauseous sulfur compounds by photocatalysis or photosensitization. Catal. Today 2007, 122, 27–38. [Google Scholar] [CrossRef]
  68. Soni, K.C.; Shekar, S.C.; Singh, B.; Gopi, T. Catalytic activity of Fe/ZrO2 nanoparticles for dimethyl sulfide oxidation. J. Colloid Interface Sci. 2015, 446, 226–236. [Google Scholar] [CrossRef]
  69. Chen, J.; Qin, Y.; Chen, Z.; Yang, Z.; Yang, W.; Wang, Y. Gas circulating fluidized beds photocatalytic regeneration of I-TiO2 modified activated carbons saturated with toluene. Chem. Eng. J. 2016, 293, 281–290. [Google Scholar] [CrossRef]
  70. Demeestere, K.; Dewulf, J.; De Witte, B.; Van Langenhove, H. Titanium dioxide mediated heterogeneous photocatalytic degradation of gaseous dimethyl sulfide: Parameter study and reaction pathways. Appl. Catal. B Environ. 2005, 60, 93–106. [Google Scholar] [CrossRef]
  71. Yu, X.; Yin, H.; Ye, J.S.; Peng, H.; Lu, G.; Dang, Z. Degradation of tris-(2-chloroisopropyl) phosphate via UV/TiO2 photocatalysis: Kinetic, pathway, and security risk assessment of degradation intermediates using proteomic analyses. Chem. Eng. J. 2019, 374, 263–273. [Google Scholar] [CrossRef]
  72. Manheim, J.M.; Milton, J.R.; Zhang, Y.; Kenttamaa, H.I. Fragmentation of saturated hydrocarbons upon atmospheric pressure chemical ionization is caused by proton-transfer reactions. Anal. Chem. 2020, 92, 8883–8892. [Google Scholar] [CrossRef] [PubMed]
  73. Vlasenko, A.; Macdonald, A.; Sjostedt, S.; Abbatt, J. Formaldehyde measurements by Proton transfer reaction–Mass Spectrometry (PTR-MS): Correction for humidity effects. Atmos. Meas. Tech. 2010, 3, 1055–1062. [Google Scholar] [CrossRef] [Green Version]
  74. Inomata, S.; Tanimoto, H.; Kameyama, S.; Tsunogai, U.; Irie, H.; Kanaya, Y.; Wang, Z. Determination of formaldehyde mixing ratios in air with PTR-MS: Laboratory experiments and field measurements. Atmos. Chem. Phys. 2008, 8, 273–284. [Google Scholar] [CrossRef] [Green Version]
  75. Jobson, B.; McCoskey, J. Sample drying to improve HCHO measurements by PTR-MS instruments: Laboratory and field measurements. Atmos. Chem. Phys. 2010, 10, 1821–1835. [Google Scholar] [CrossRef] [Green Version]
  76. Warneke, C.; Veres, P.; Holloway, J.; Stutz, J.; Tsai, C.; Alvarez, S.; Rappenglueck, B.; Fehsenfeld, F.; Graus, M.; Gilman, J.; et al. Airborne formaldehyde measurements using PTR-MS: Calibration, humidity dependence, inter-comparison and initial results. Atmos. Meas. Tech. 2011, 4, 2345–2358. [Google Scholar] [CrossRef] [Green Version]
  77. Wisthaler, A.; Apel, E.; Bossmeyer, J.; Hansel, A.; Junkermann, W.; Koppmann, R.; Meier, R.; Müller, K.; Solomon, S.; Steinbrecher, R.; et al. Intercomparison of formaldehyde measurements at the atmosphere simulation chamber SAPHIR. Atmos. Chem. Phys. 2008, 8, 2189–2200. [Google Scholar] [CrossRef] [Green Version]
  78. Salthammer, T.; Mentese, S. Comparison of analytical techniques for the determination of aldehydes in test chambers. Chemosphere 2008, 73, 1351–1356. [Google Scholar] [CrossRef] [PubMed]
  79. Cui, L.; Zhang, Z.; Huang, Y.; Lee, S.C.; Blake, D.R.; Ho, K.F.; Wang, B.; Gao, Y.; Wang, X.M.; Louie, P.K.K. Measuring OVOCs and VOCs by PTR-MS in an urban roadside microenvironment of Hong Kong: Relative humidity and temperature dependence, and field intercomparisons. Atmos. Meas. Tech. 2016, 9, 5763–5779. [Google Scholar] [CrossRef] [Green Version]
Sustainability 13 04821 g001 550
Figure 1. Byproducts of TiO2 photocatalytic degradation of DMS, with LDLS lamp excitation.
Figure 1. Byproducts of TiO2 photocatalytic degradation of DMS, with LDLS lamp excitation.
Sustainability 13 04821 g001
Sustainability 13 04821 g002 550
Figure 2. Byproducts of TiO2/AC (1:1) photocatalytic degradation of DMS with LDLS lamp excitation.
Figure 2. Byproducts of TiO2/AC (1:1) photocatalytic degradation of DMS with LDLS lamp excitation.
Sustainability 13 04821 g002
Sustainability 13 04821 g003 550
Figure 3. Byproducts of TiO2/AC (1:5) photocatalytic degradation of DMS with LDLS lamp excitation.
Figure 3. Byproducts of TiO2/AC (1:5) photocatalytic degradation of DMS with LDLS lamp excitation.
Sustainability 13 04821 g003
Sustainability 13 04821 g004 550
Figure 4. Proposed photocatalytic oxidation pathways of DMS considering direct electron transfer of hole and hydroxyl radical oxidation.
Figure 4. Proposed photocatalytic oxidation pathways of DMS considering direct electron transfer of hole and hydroxyl radical oxidation.
Sustainability 13 04821 g004
Sustainability 13 04821 g005 550
Figure 5. Byproducts of TiO2 photocatalytic degradation of DMS.
Figure 5. Byproducts of TiO2 photocatalytic degradation of DMS.
Sustainability 13 04821 g005
Sustainability 13 04821 g006 550
Figure 6. Byproducts of TiO2/AC (1:1) photocatalytic degradation of DMS by LDLS lamp as a function of temperature.
Figure 6. Byproducts of TiO2/AC (1:1) photocatalytic degradation of DMS by LDLS lamp as a function of temperature.
Sustainability 13 04821 g006
Sustainability 13 04821 g007 550
Figure 7. Process diagram of the photocatalytic reaction system setup.
Figure 7. Process diagram of the photocatalytic reaction system setup.
Sustainability 13 04821 g007
Table
Table 1. Summary of the removal efficiencies of DMS f R E for TiO2, TiO2/AC (1:1) and TiO2/AC (1:1) and byproduct yields χ .
Table 1. Summary of the removal efficiencies of DMS f R E for TiO2, TiO2/AC (1:1) and TiO2/AC (1:1) and byproduct yields χ .
Substrate f RE /%χCH2O/%χCH3COCH3/%χCH3SSCH3/%
TiO247.45.20.5−0.5
TiO2/AC (1:1)22.912.30.5−0.2
TiO2/AC (1:5)13.411.20.2−0.4
Table
Table 2. The removal efficiency and byproduct yields for DMS with LDLS light excitation on TiO2 at 20 temperature, 30 ∘ C, 50 ∘ C, and 70 ∘ C.
Table 2. The removal efficiency and byproduct yields for DMS with LDLS light excitation on TiO2 at 20 temperature, 30 ∘ C, 50 ∘ C, and 70 ∘ C.
T/ ∘ CfCH3SCH3/%χCH2O/%χCH3COCH3/%χCH3SSCH3/%
2058.112.83.65.2
3050.118.12.48.4
5049.221.015.55.4
7048.17.44.612.4
Table
Table 3. Physical properties of product molecules.
Table 3. Physical properties of product molecules.
NameFormulaVapor PressureSolubilityBoiling PointDipole Moment
Carbon monoxideCO>35 atm2%−191.5 ∘ C0.122 D
Carbon dioxideCO256.5 atm0.2% (25 ∘ C)78.48 ∘ C-
MethaneCH4 4.7 × 10 4 kPa (25 ∘ C)3.5 mL/100 mL at (17 ∘ C)−161 ∘ C at 101.32 kPa-
FormaldehydeCH2O1.40 kPa at 25 ∘ C4.00 × 10 + 5 mg/L at 20 ∘ C−21 ∘ C at 101.32 kPa2.330 D
Dimethyl sulfideCH3SCH353.7 kPa (at 20 ∘ C)22 mg/mL at 25 ∘ C37.2 ∘ C at 101.32 kPa1.499 D
AcetoneC3H6O9.39 kPa (0 ∘ C)
30.6 kPa (25 ∘ C)
374 kPa (100 ∘ C)
2.8 MPa (200 ∘ C)		Miscible56.05 ∘ C ( 44 ∘ C)2.91 D
Dimethyl disulfideCH3SSCH33.8 kPa (at 25 ∘ C)2.5 g/L (20 ∘ C)110 ∘ C1.50 D
* Data were acquired from PubChem (https://pubchem.ncbi.nlm.nih.gov/ accessed on 15 March 2021).
Table
Table 4. The removal efficiency and byproduct yields for DMS degradation with LDLS light excitation on TiO2/AC (1:1) at 20, 30, 50, and 70 ∘ C.
Table 4. The removal efficiency and byproduct yields for DMS degradation with LDLS light excitation on TiO2/AC (1:1) at 20, 30, 50, and 70 ∘ C.
T/ ∘ CfCH3SCH3/%χCH2O/%χCH3COCH3/%χCH3SSCH3/%
2028.29.31.3−0.1
3032.98.91.6−0.6
5016.031.721.21.0
7011.120.417.11.7
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Yu, W.; in `t Veld, M.; Bossi, R.; Ateia, M.; Tobler, D.; Feilberg, A.; Bovet, N.; Johnson, M.S. Formation of Formaldehyde and Other Byproducts by TiO2 Photocatalyst Materials. Sustainability 2021, 13, 4821. https://doi.org/10.3390/su13094821

AMA Style

Yu W, in `t Veld M, Bossi R, Ateia M, Tobler D, Feilberg A, Bovet N, Johnson MS. Formation of Formaldehyde and Other Byproducts by TiO2 Photocatalyst Materials. Sustainability. 2021; 13(9):4821. https://doi.org/10.3390/su13094821

Chicago/Turabian Style

Yu, Weijia, Marten in `t Veld, Rossana Bossi, Mohamed Ateia, Dominique Tobler, Anders Feilberg, Nicolas Bovet, and Matthew S. Johnson. 2021. "Formation of Formaldehyde and Other Byproducts by TiO2 Photocatalyst Materials" Sustainability 13, no. 9: 4821. https://doi.org/10.3390/su13094821

APA Style

Yu, W., in `t Veld, M., Bossi, R., Ateia, M., Tobler, D., Feilberg, A., Bovet, N., & Johnson, M. S. (2021). Formation of Formaldehyde and Other Byproducts by TiO2 Photocatalyst Materials. Sustainability, 13(9), 4821. https://doi.org/10.3390/su13094821

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop