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Thus, a photocatalyst that could degrade these contaminations should be developed and used together with the plastic degradation photocatalyst. 22/2022) - Chu - 2022 - Advanced Energy Materials - Wiley Online Library Advanced Energy Materials Volume 12, Issue 22 2270089 Cover Picture Free Access https://doi.org/10.3390/mi12080907, Subscribe to receive issue release notifications and newsletters from MDPI journals, You can make submissions to other journals. Despite the advantages of photocatalysis and extensive efforts devoted to plastic photodegradation to date, there are still several major challenges as follows: The authors extended their appreciation to Nanyang Technological University Singapore for support via ACE award. Zhang, J.; Tian, B.; Wang, L.; Xing, M.; Lei, J. Bickley, R.I.; Gonzalez-Carreno, T.; Lees, J.S. The mechanisms of photodegradation of polymers in general were then revisited. Zan L., Tian L., Liu Z., Peng Z. Therefore, we present this short review to recap the photocatalytic degradation mechanism and to discuss the research efforts on photodegradation of various plastic polymers, aiming to inspire more research ideas to address this urgent challenge of plastic waste. An official website of the United States government. However, an intensive research effort may be necessary for developing such a photocatalyst. Rajaambal S., Sivaranjani K., Gopinath C.S. UV radiation is known as the most damaging source to polymers owing to its high energy. However, the hazard of discarding waste plastic, so-called "white pollution", is becoming more and more severe. In this review, the recent advances in plastic conversion through photocatalysis have been comprehensively summarized. Some in situ/operando characterizations could be useful, such as Raman spectroscopy, photoluminescence spectroscopy, and high-resolution soft X-ray absorption spectroscopy. We use cookies on our website to ensure you get the best experience. Considering the low economic viability of such a process, a new method to introduce photocatalyst into plastic waste is needed. In this perspective, we highlight the effect of photocatalytic approaches toward the generation of low carbon number organic products (Cn products, n 8) from waste plastics, which can proceed under an inert or aerobic atmosphere. Herein, we revisit the concept of catalytic photodegradation of plastic wastes. In the initiation step, the existence of chromophore group, which absorbs the incident light due to energy matching, in the polymers structure is important to act as the photo-initiator [8]. [53]. Chatterjee, D.; Dasgupta, S. Visible light induced photocatalytic degradation of organic pollutants. SnO 2 nanoparticles were synthesized by a polymeric precursor method, yielding specific surface . ; Aslam, M.R. Enhanced solid-phase photocatalytic degradation of polyethylene by TiO, Li, S.; Xu, S.; He, L.; Xu, F.; Wang, Y.; Zhang, L. Photocatalytic Degradation of Polyethylene Plastic with Polypyrrole/TiO, Liang, W.; Luo, Y.; Song, S.; Dong, X.; Yu, X. Pure PP, PP/OMT, and PP/TiO2 composites as control samples were prepared for comparison. (b) Weight loss curve of PS-TiO2 and PS-(TiO2/CuPc) samples. Herein, spent LIBs and BCPs are copyrolyzed in a sealed, The recent COVID-19 pandemic has resulted in the massive discard of pandemic-related plastic wastes, causing serious ecological harm and a high societal burden. A new polystyreneTiO, Zan L., Wang S., Fa W., Hu Y., Tian L., Deng K. Solid-phase photocatalytic degradation of polystyrene with modified nano-TiO, Fa W., Zan L., Gong C., Zhong J., Deng K. Solid-phase photocatalytic degradation of polystyrene with TiO, Lei Y., Lei H., Huo J. Furthermore, it was found that the particle size of TiO2 plays an important role, and extra fine TiO2 is more favourable than large particles for photocatalytic degradation. Plastic waste becomes an immediate threat to our society with ever-increasing negative impacts on our environment and health by entering our food chain. Most of the current work involves dissolving plastics followed by mixing with photocatalyst to make a composite, which is then photodegraded. Photocatalytic reforming of lignocellulosic biomass is an emerging approach to produce renewable H2 that is less energy demanding than water splitting and generates highpurity H2 without O2 production. The GGA+U approach is improved in terms of the energy gap of material and impurity state in the gap. UV-B has a wavelength from 280 to 315 nm, whereas UV-A has a wavelength from 315 to 400 nm. As displayed in Figure 16c, the molecular weight (Mw) distribution curve peak shifts to the lower value from LDPE towards the LDPE/PAM-g-TiO2-UV sample, indicating that the PAM-g-TiO2 has the highest activity towards LDPE degradation under UV irradiation. Liang, Y.; Tan, Q.; Song, Q.; Li, J. those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). In addition, the hydroperoxides react with another hydroperoxide to form polymer alkoxy radicals, polymer peroxide radicals, and water (Path 5). Energy Mater. trbac D., Aggelopoulos C.A., Goran ., Dimitropoulos M., Novakovi M., Iveti T., Yannopoulos S.N. Photoelectrochemical conversion of plastic waste into high-value chemicals coupling hydrogen production. Arai, T.; Horiguchi, M.; Yanagida, M.; Gunji, T.; Sugihara, H.; Sayama, K. Reaction Mechanism and Activity of WO3-Catalyzed Photodegradation of Organic Substances Promoted by a CuO Cocatalyst. https://doi.org/10.3390/mi12080907, Lee QY, Li H. Photocatalytic Degradation of Plastic Waste: A Mini Review. Cromer D.T., Herrington K. The Structures of Anatase and Rutile. Senasu T., Hemavibool K., Nanan S. Hydrothermally grown CdS nanoparticles for photodegradation of anionic azo dyes under UV-visible light irradiation. Hence, different initiation steps have been undertaken for various conditions in different polymers to form the free radicals. instance of. Purple dotted box: Initiation step; black dashed boxes: Propagation step; orange dash-dotted boxes: Termination step. To this end, photodegradation is perfect as sunlight is known to be an effective energy source to degrade plastic. Solar-driven photocatalytic reforming of lignocellulose to, By clicking accept or continuing to use the site, you agree to the terms outlined in our. Rao H., Lu Z., Liu X., Ge H., Zhang Z., Zou P., He H., Wang Y. ; Hadjltaief, H.B. The authors attributed the decreased efficiency to the carbon-coated layer decreasing the amount of UV light reaching the surface of the particles, and in turn reducing the hydroxyl groups on the surface of TiO2. Zou L., Wang H., Wang X. As expected, the degradation efficiency is always relatively higher for the latter. A comparison with low molecular weight compounds. Plastic polymers including PE (LDPE, HDPE), PP, PS, and PVC are described in our review as they constitute the worlds most common plastic and most of them are challenging to be recycled. In the range of 300400 nm, TiO2/CuPc shows a much higher photovoltage, suggesting a higher charge separation efficiency and longer excitations lifetime than that of TiO2. future research directions and describes possible research applications. Environ. High photocatalytic degradation activity of polyethylene containing polyacrylamide grafted TiO. Visible light-driven photocatalytic degradation performance for methylene blue with different multi-morphological features of ZnS. To increase the photocatalytic degradation activity under visible light, the energy band gap needs to be reduced. From the experimental results, modified TiO2 photocatalysts showed a much higher photocatalytic degradation efficiency than pure TiO2. Fa W., Gong C., Tian L., Peng T., Zan L. Enhancement of photocatalytic degradation of poly(vinyl chloride) with perchlorinated iron (II) phthalocyanine modified nano-TiO, Yang C., Deng K., Peng T., Zan L. Enhanced Solid-Phase Photocatalytic Degradation Activity of a Poly(vinyl chloride)-TiO, Yang C., Tian L., Ye L., Peng T. Enhancement of photocatalytic degradation activity of poly(vinyl chloride)-TiO, Zhang Y., Sun T., Zhang D., Shi Z., Shi Z., Zhang X., Li C., Wang L., Song J., Lin Q. scientific article published on 22 April 2022. Likewise, the singlet oxygen produced also leads to the formation of ROOH by the oxidation of an olefin containing allylic hydrogen, as depicted in Figure 2b. Aragaw T.A. Schematic carrier recombination process in (d) anatase and (e) rutile TiO2. These ROSs capture hydrogen atoms in PP polymer chains and then generate CH2(CH3)C macro molecule radicals, followed by chain scission, as detailed in Figure 12c. ; Oasmaa, A.; Pihkola, H.; Deviatkin, I.; Tenhunen, A.; Mannila, J.; Minkkinen, H.; Pohjakallio, M.; Laine-Ylijoki, J. Pyrolysis of plastic waste: Opportunities and challenges. Decomposition of a large plastic polymer to small molecules is mechanistically complicated. Multiple requests from the same IP address are counted as one view. Lee, J.; Lee, Y.; Song, H.; Jang, D.; Choa, Y. Synthesis and characterization of TiO, Mack, J.M. The modified photocatalysts can effectively improve the migration and separation of TiO2 photogenerated electrons thanks to the built-in electric field at the heterojunction, which inhibits the recombination of the photogenerated charge carriers, and thus further improves the photocatalytic degradation rate. In the propagation step [8,16], polymer macro radicals formed through photo-initiation react with the oxygen to form polymer peroxyl radicals (Path 2). Photocatalytic processes are emerging as green and promising approaches to upcycle plastics into valueadded products under mild conditions using sunlight as the energy source. Conclusively, olefins and ketones are the expected products of the termination reactions [16]. Ultraviolet radiation consists of electromagnetic waves with a wavelength between 100 and 400 nm [, UV radiation is known as the most damaging source to polymers owing to its high energy. Photocatalytic degradation of polypropylene film using TiO. Photodegradation of doped TiO2 composite films including Fe/Ag dually doped TiO2, Ag-doped TiO2, and Fe doped TiO2 were investigated [74]. Mater. The plastics with SPI number 1 to 7, including polyethylene terephthalate (PET), polyethylene (PE), polyvinyl chloride (PVC), polypropylene (PP), polystyrene (PS), etc., are present in Table 1 [1]. As a library, NLM provides access to scientific literature. Ultraviolet radiation consists of electromagnetic waves with a wavelength between 100 and 400 nm [12], which is further divided into three major sub-regions. However, the impurities or structural defects in the polymers, as well as carbonyl groups within the backbone of the polymer can act as chromophores to carry out the photo-initiation [6]. Ali, S.S.; Elsamahy, T.; Koutra, E. Degradation of conventional plastic wastes in the environment: A review on current status of knowledge and future perspectives of disposal. FOIA Zhang, J.; Zhou, P.; Liu, J.; Yu, J. Developing efficient approach to recycle the plastic has been an urgent demand for realizing a sustainable circular economy. Rahimi, A.; Garca, J.M. The photogenerated electrons and holes in TiO2 can react with the absorbed H2O or O2 to produce various reactive oxygen species (ROSs) including O2, HOO, HO, etc. Furthermore, due to the different molecular structures, it is found that the degradation of PS-TiO2/CuPc was slower than PE-TiO2/CuPc. (c) Weight loss of the pure PVC and PVC-TiO2 (1.5 wt%) composite film during irradiation in air (filled symbols) or N2 (open symbols) atmosphere [60]; reprinted from [60] with permission from Elsevier. (b) Apparent absorbance of the composite films at = 350 nm as a function of the film thickness. Licensee MDPI, Basel, Switzerland. . Recent developments in solar H, Schneider J., Matsuoka M., Takeuchi M., Zhang J., Horiuchi Y., Anpo M., Bahnemann D.W. Understanding TiO. 2021; 12(8):907. Moreover, the TiO2/CuPc sample displays a broader range of photo response. Find support for a specific problem in the support section of our website. In contrast, the rest of the samples show a much smoother surface, suggesting mild degradation. It yields an energetic sequence consistent with the experiments, Erutile < Eanatase, for 5 < U < 8 eV. Structure of (c) s-triazine and (d) tri-s-triazine as the primary building blocks of graphitic carbon nitride with C atoms in grey and N atoms in blue [50]; reprinted from [50] with permission from Elsevier. Those reactions can be initiated by physical factors such as direct UV initiated photolysis of C-C and C-H bond or by chemical factors such as the residues of catalyst used, incorporation of carbonyl groups, and introduction of peroxides or unsaturation site [13]. In the oxidative reaction, holes in the VB of photocatalyst react with the water in the air to form proton and hydroxyl radicals, as depicted in Equation (5). By parsing photocatalytic plastic conversion process, we demonstrate the currently available routes for processing plastic, including plastic photodegradation, tandem decomposition of plastic and CO 2 reduction, selective plastic oxidation, as well as photoreforming of plastic. Notably, the photocatalytic activity also greatly depends on other factors such as the geometry [32], the substrates [33], and the oxygen vacancy/defects density [37]. In order to be human-readable, please install an RSS reader. Inclusion in an NLM database does not imply endorsement of, or agreement with, Photocatalytic Conversion of Plastic Waste: From Photodegradation to Photosynthesis. Zhang, K.; Hamidian, A.H.; Tubi, A.; Zhang, Y.; Fang, J.K.H. High Efficient Photodegradation and Photocatalytic Hydrogen Production of CdS/BiVO. Lastly, in the termination step [8], the free radicals produced react with each other to undergo the crosslinking reaction for the formation of inert products (Path 9). The singlet oxygen is produced due to the quenching of the excited triplet state of suitable sensitizers (, A singlet oxygen could react with the product of a Norrish reaction, which is a photochemical reaction taking place with ketones and aldehydes. Surgical face masks as a potential source for microplastic pollution in the COVID-19 scenario. In this review, the recent advances in plastic conversion through photocatalysis have been comprehensively summarized. Three types of samples were prepared by mixing carbon-coated TiO2 and PP with the decreasing carbon content from PP5Ti (30.6 wt%), PP10Ti (11.6 wt%), PP30Ti (2.7 wt%) to PPDTi (0 wt.%), with reference to pure PP. However, the photocurrent of TiO2/CuPc is much larger than that of TiO2. Approximately 70% of global municipal solid waste is lost to landfills or the environment each year, an emblem of our increasingly unsustainable economic system in which materials and energy are, Lignocellulose is Earths most abundant form of biomass and its valorization to H2 is a key objective for the generation of renewable fuels. The photocatalytic degradation of PS plastic [(C8H8)n, as shown in the inset of Figure 8a] with TiO2 as photocatalyst was investigated in the ambient air under UV irradiation [54]. Shang, J.; Chai, M.; Zhu, Y. Photocatalytic Degradation of Polystyrene Plastic under Fluorescent Light. Geuskens G., David C. The photo-oxidation of polymers. Mentioning: 16 - The continuous rise in plastic waste raises serious concerns about the ensuing effects on the pollution of global environment and loss of valuable resources. Interfaces 2018, 10, 9, 8077-8085 https://www.mdpi.com/openaccess. stated in. The experiment using TiO2/CuPc as photocatalyst to degrade the PE plastic has been conducted, and the results showed that PE-TiO2/CuPc has a higher photocatalytic degradation rate than PE-TiO2 [72]. Comparative Solid Phase Photocatalytic Degradation of Polythene Films with Doped and Undoped TiO, An Y., Hou J., Liu Z., Peng B. Sunlight is known to be the natural energy source that degrades plastic waste at a very slow rate. SPI number for different types of plastic and the recovery rate from the total solid plastic waste [1]. For instance, the UV-VIS absorption spectrum of TiO2/CuPc shows a broad absorption peak in the visible range of 500 to 650 nm thanks to CuPc, as depicted in Figure 9a. All authors have read and agreed to the published version of the manuscript. ; Chuy, G.; dos Santos, C.; Brum, L.F.W. [(accessed on 21 February 2021)]; Plastics Market Size, Share & Trends Report, 20202027. https://doi.org/10.3390/mi12080907, Lee, Qian Ying, and Hong Li. Rajaambal, S.; Sivaranjani, K.; Gopinath, C.S. Please note that many of the page functionalities won't work as expected without javascript enabled. ; Robertson, J. Photodegradation of PS-TiO2 film. Author to whom correspondence should be addressed. The photocatalytic degradation rate of PE (see inset of Figure 15a for molecular structure) is found not linearly proportional to the TiO2 concentration [71]. Fa, W.; Gong, C.; Tian, L.; Peng, T.; Zan, L. Enhancement of photocatalytic degradation of poly(vinyl chloride) with perchlorinated iron (II) phthalocyanine modified nano-TiO, Yang, C.; Deng, K.; Peng, T.; Zan, L. Enhanced Solid-Phase Photocatalytic Degradation Activity of a Poly(vinyl chloride)-TiO, Yang, C.; Tian, L.; Ye, L.; Peng, T. Enhancement of photocatalytic degradation activity of poly(vinyl chloride)-TiO, Zhang, Y.; Sun, T.; Zhang, D.; Shi, Z.; Shi, Z.; Zhang, X.; Li, C.; Wang, L.; Song, J.; Lin, Q. Moreover, anatase exhibits an indirect bandgap, while rutile and brookite show direct bandgaps, as illustrated in Figure 5d,e. The mechanism involves three main steps, i.e., initiation, propagation, and termination, as summarized in Figure 3. ; da Silva, W.L. Overall, the degradation of doped TiO2 was greater than that of the undoped TiO2, and Fe/Ag dually doped TiO2 shows the highest degradation rate under UV light among all, as shown in Figure 15c. ; Ilyas, H.; Khan, A.A.; Awan, M.A. Visit our dedicated information section to learn more about MDPI. Bickley R.I., Gonzalez-Carreno T., Lees J.S., Palmisano L., Tilley R.J.D. When the photocatalytic degradation of PS plastic was carried out with FePc-TiO2, HADPG-TiO2 or TiO2/CuPc as photocatalyst, it was found that these modified TiO2 had a widened absorption under visible light. Zan, L.; Tian, L.; Liu, Z.; Peng, Z. Guo, Y.; Clark, S.J. Hence, hydroxyl radical is known as the essential element in photocatalysis. Anatase TiO2 has a CBM at the energy level of ECB = 0.51 V, while rutile TiO2 has CBM at ECB = 0.31 V [33]. ; Tsuchiya, H.; Ghicov, A.; Yasuda, K.; Hahn, R.; Bauer, S.; Schmuki, P. TiO, Yu, Y.; Zhang, P.; Guo, L.; Chen, Z.; Wu, Q.; Ding, Y.; Zheng, W.; Cao, Y. With the wavelength ranging from 100 to 280 nm, UV-C is fully absorbed by the ozone in the atmosphere. ; Jacobs, D.; Perry, L.; Goodwin, D.; White, C.; Watson, S.; Sung, L. Temperature and light intensity effects on photodegradation of high-density polyethylene. Thus, a key to increase the recycling rate of plastic waste, and thus less disposal of plastic waste to landfill, is to develop a decentralized degradation process that could leverage renewable energies as the driving force. Photocatalytic processes are emerging as green and promising approaches to upcycle plastics into valueadded products under mild conditions using sunlight as the energy source. One can see that, after 500-h of illumination, PP30Ti and PPDTi show a very rough surface with very large cavities. The demand for disposable plastic products including food containers, plastic bags, and poly mailbags in the packaging industry which are made from plastic has also been growing rapidly since more people are staying at home, calling for food delivery, and online shopping particularly in the current pandemic [4]. Moreover, the weight loss percentage is higher in air ambient compared to that in nitrogen ambient (Figure 10c). Thus, its efficiency would be low if light penetration is blocked by the non-transparent contaminations. Photocatalysis is used in many applications such as removal of pollutants and bacteria [18], energy conversion [19], and water splitting for green hydrogen generation [20]. The global plastic production was about 2 million tons in the year 1950, which is trivial compared to the annual production nowadays (368 million tons as of 2019) [2]. Most of the plastic wastes are generated in a widespread manner and contaminated by various other wastes such as food wastes, wood waste, and chemical waste. Consequently, hydroxyl radicals will decompose organic pollutants into the water and carbon dioxide. Owing to strong O 2p-Ti 3d hybridizations, the valance bands contain O 2p and some Ti 3d states. Yousif E., Haddad R. Photodegradation and photostabilization of polymers, especially polystyrene: Review. Understanding plastic degradation and microplastic formation in the environment: A review. (c) The schematic charge separation mechanism of TiO2/CuPc sample under visible and UV light radiation [55]; reprinted (adapted) from [55] with permission from the American Chemical Society. As such, the photogenerated electron and hole are separated and then utilized to reduce oxygen and to oxidize PS molecule, respectively. Moreover, the photocatalytic activity of PE-TiO2 can be improved using modified TiO2 photocatalysts such as multiwalled carbon nanotube (MWCNT)-TiO2 composite (TiO2-MWCNTs) [75], polypyrrole(PPy)-TiO2 composite (PPy/TiO2) [76], and polyacrylamide grafted TiO2 (PAM-g-TiO2) [77]. Photoreforming, as a simple and low-energy, The continuous increase in manufacturing coupled with the difficulty of recycling of plastic products has generated huge amounts of waste plastics. Having the valance band maximum (VBM) more positive than 1.23 eV, showing that the oxidation ability is sufficient in oxidizing water. ZnO as a Functional Material, a Review. A singlet oxygen could react with the product of a Norrish reaction, which is a photochemical reaction taking place with ketones and aldehydes. The sun emits energy over a broad range of wavelengths from ultraviolet spectrum (UV), visible spectrum (Vis-), to infrared spectrum (IR) with decreasing energy. Moreover, the selectivities of these catalysts are crucial from an economical perspective. ; Zheng, Y.; Ding, J. Synthesis, surface modification and photocatalytic property of ZnO nanoparticles. Comparative Solid Phase Photocatalytic Degradation of Polythene Films with Doped and Undoped TiO, An, Y.; Hou, J.; Liu, Z.; Peng, B. articles published under an open access Creative Common CC BY license, any part of the article may be reused without Here we demonstrate a photocatalytic method to oxidize polystyrene to aromatic oxygenates under visible light irradiation using heterogeneous graphitic carbon nitride catalysts. This review concludes with a personal perspective for potential . (A) Keyword clouds were generated to provide a correlation between most researched processes and plastic types. Shi, H.; Magaye, R.; Castranova, V.; Zhao, J. Titanium dioxide nanoparticles: A review of current toxicological data. Different phases have different symmetries of the octahedral-shaped TiO6 fundamental building blocks [28]. The oxidation-reduction ability of a photocatalyst depends on its energy band position w.r.t. Most single-use face masks are made of, Industrial & Engineering Chemistry Research, Chemical recycling of is one of the promising ways for waste plastics disposal. This enhanced the ability for PS degradation under visible light, subsequently increasing the photocatalytic degradation efficiency under solar irradiation (Figure 9b). PAM absorbs moisture from the atmosphere due to its high hydrophilicity, which results in the weight loss of PAM-g-TiO2 sample before 100 C on the thermogravimetric analysis curve, as shown in Figure 16a. Then, the superoxide will undergo further reduction to produce hydrogen peroxides, which may generate hydroxides and hydroxyl radicals through the reaction with the electrons, as shown in Equation (4) [33]. Visible range photocatalysts for solid phase photocatalytic degradation of polyethylene and polyvinyl chloride. Photodegradation of PS-(TiO2/CuPc) film.
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