TiO2 Photocatalytic Oxidation Research Articles

Efficacy and Economic Benefits of Nano TiO2 Photocatalytic Advanced Oxidation Technology in Solid Waste Treatment

In order to assess the application value of nano TiO2 photocatalytic advanced oxidation technology in the field of solid waste treatment and improve the efficiency of waste disposal, this study investigates the preparation of TiO2/ZnIn2S4 composite photocatalysts using an in-situ growth method. Subsequently, this photocatalyst is applied to urban solid waste treatment schemes to degrade solid waste and organic pollutants in wastewater. The results indicate that, at a pH value of 7.5, the composite material exhibits the optimal photocatalytic degradation performance, achieving a degradation rate of 90%. Following the urban solid waste treatment scheme, the greenhouse gas emissions per ton of municipal solid waste range from 50 to 100 kg, resulting in a 90% reduction in greenhouse gas emissions. The calculated payback period for this waste treatment scheme is 5 years. The findings suggest that this treatment approach effectively reduces greenhouse gas emissions, enhances resource recovery rates, and demonstrates favorable economic benefits for application in small to medium-sized urban areas. This research provides valuable insights for the application of nano TiO2 photocatalytic technology in the field of solid waste treatment.

Pilot‐scale photocatalytic detoxification and disinfection of hazardous medical wastewater

AbstractBACKGROUNDTreatment of liquid hazardous medical wastewater produced by healthcare laboratories is a global matter that has been inadequately addressed. In this study, the potential of heterogeneous and homogeneous photocatalytic oxidation to detoxify and disinfect such effluents was investigated. Experiments were performed using two toxic effluents and one of simultaneous toxic and infectious composition in pilot scale, in a novel photocatalytic inactivation system.RESULTSPhotocatalytic experimental runs performed with both toxic effluents showed that photo‐Fenton‐assisted TiO2 photocatalytic oxidation under optimal conditions was the most efficient process among the tested ones, when the initial dissolved organic carbon values (DOC0) ranged from 100 to 1000 mg L−1. Furthermore, the potential of catalyst reuse was examined and verified for five sequential runs. Moreover, phytotoxicity was either eliminated or significantly reduced after photocatalytic processing under optimal conditions in the case of the second wastewater of toxic composition, while ecotoxicity showed a similar trend, highlighting the importance of extended mineralization for the removal of toxicity. The performance of the pilot photocatalytic inactivation system concerning the inactivation of bio‐pollutants was tested on five different types of microbes. Four of them were completely inactivated in relatively short periods, while survival of the more resistant bacterial endospores was found to be decreased to >99% after 5 h of treatment.CONCLUSIONToxic and infectious hazardous medical effluents are highly recalcitrant targets in terms of mineralization, detoxification and inactivation. However, photocatalytic oxidation may serve as an efficient processing tool, providing alternative or complementary solutions to this highly challenging issue. © 2023 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Efficient removal of anti-HIV drug - maraviroc from natural water by peroxymonosulfate and TiO2 photocatalytic oxidation: Kinetic studies and identification of transformation products

In this study photochemical transformation of the antiretroviral pharmaceutical maraviroc under the simulated UV–Vis radiation was presented. The drug was shown to be extremely photo-resistant, with a half-life over 250 h, which is particularly significant, considering its presence in the aquatic environments. Addition of the natural river water matrix substantially increased the degradation rate, albeit the process led to formation of numerous phototransformation products. Due to high photostability and presumable environmental persistence of maraviroc, a photocatalytic method of its elimination was proposed. Although titanium dioxide alone presented acceptable results, its combination with peroxymonosulfate enormously accelerated the degradation process, increasing it over 67 000 times in comparison with the direct photolysis. Substitution of ultrapure water with river water resulted in inhibition of the PMS-driven processes, however the decomposition efficiency was still very high. Noteworthy, majority of the identified photoproducts were still present after termination of irradiation in all the experiments, which may indicate necessity of ecotoxicological assessment of those compounds.

Destruction of oxytetracycline using a microwave-assisted fused TiO2 photocatalytic oxidation system

Destruction of oxytetracycline using a microwave-assisted fused TiO2 photocatalytic oxidation system

Multiwell photocatalytic microreactor device integrating drug biotransformation modeling and sample preparation on a MALDI target

Metabolic conversion of drugs to chemically reactive products, known as bioactivation, is considered to underlie the adverse drug reactions such as idiosyncratic hepatotoxicity. As bioactivation of most drugs involves phase I oxidation, UV-induced TiO2 photocatalytic oxidation (UV/TiO2-PCO) can be used as a fast, simple and inexpensive non-enzymatic method of oxidative metabolism simulation allowing for rapid preliminary screening of candidate drugs for reactive metabolite formation. We developed and evaluated a novel prototype 96-well on-target UV/TiO2-photocatalytic microreactor setup (PCμR96) that integrates drug metabolism simulation and sample preparation directly on a MALDI target. PCμR96 allows to sequentially perform UV/TiO2-PCO of xenobiotics, GSH or protein adduct formation, protein digestion and sample concentration, followed by surface- or matrix-assisted laser desorption ionization (SALDI/MALDI) mass spectrometry (MS). Amodiaquine (AQ), a well-studied antimalarial drug that is known to undergo oxidative biotransformation, was selected as a model compound. Oxidation products of AQ and their protein adducts were obtained using PCμR96 and identified by SALDI and MALDI MS/MS analysis. The achieved AQ oxidation products were in good agreement with the known AQ metabolites produced in biological systems. Two of the products were proved to be reactive towards cysteyl thiols of human globin.

Defect-enhanced photocatalytic removal of dimethylarsinic acid over mixed-phase mesoporous TiO2

Much attention has been paid to the pollutant dimethylarsenic acid (DMA), because of its high toxicity even at very low doses. Although TiO2 photocatalytic oxidation (PCO) is one of the few effective methods for treating DMA-containing water, the efficient decomposition of DMA and simultaneous removal of toxic arsenic species remains a significant but challenging task. Here, defective mesoporous TiO2 with mixed-phase structure was synthesized and used as both photocatalyst and adsorbent for DMA removal. Due to the reduced band-gap and enhanced separation of photogenerated charge carriers, the oxygen-deficient TiO2 nanostructures exhibited 4.2 times higher PCO efficiency than commercial TiO2 (P25). More importantly, the high surface area of the mesoporous TiO2 provided sufficient active sites for in-situ adsorption and reaction, resulting in the efficient removal of as-formed As(V). Combining the experimental and characterization results, the different roles of reactive species during PCO reactions were clarified. In the presence of hole (h+) as the dominant oxidation species, DMA was demethylated and transformed into MMA. Thereafter, MMA was subsequently reduced to As(III) by photo-generated electrons. Superoxide radicals (O2•–) played a significant role in oxidizing As(III) into As(V), which was finally adsorptively removed by the mesoporous TiO2.

Synergistic effect of TiO2 photocatalytic advanced oxidation processes in the treatment of refinery effluents

Different types of photolytic and photocatalytic advanced oxidation processes (AOPs) were used for treatment of refinery effluents from bitumen production. The treatment efficiency was evaluated by analyzing chemical oxygen demand (COD), biological oxygen demand (BOD5), volatile organic compounds (VOCs) and sulfide ions concentration. The studies revealed a synergistic effect of application of external oxidants (O3, H2O2, O3/H2O2) with TiO2 and UV applied for improved COD and BOD5 reduction as well as the degradation of the VOCs present in the effluents. Among studied processes a photocatalytic process combined with peroxone (TiO2/UV/O3/H2O2) was the optimal and the most economical technology. It allows to reduce 38 and 32% of COD and BOD5 respectively and degrade 84% of total VOCs in 280 min of treatment. At this conditions the reduced COD exceeds over 30% a theoretical value based on the dose of oxidants, which proves the importance of photocatalysis in the developed technology. The sulfide ions were completely depleted in all experiments in the first 30 min of treatment. The addition of TiO2 in the AOPs technology revealed a decrease in the process cost using less amount of chemicals achieving similar treatment efficiency when comparing with photolytic and non-catalytic technologies. The application of these technologies can be conducted in two alternative scenarios; whether to deplete the sulfides ions concentration or to maximize the treatment efficiency. In both options, the technologies studied are promising as a pre-treatment before other types of AOPs effective at neutral/acidic pH values or before a biological treatment stage. Further studies should be developed, by scaling up the process to a pilot scale in a real case scenario to check the possibility of its implementation in the industrial practice.

Rapid determination of dye concentration in wastewater by TiO2-KMnO4 synergistic photocatalytic oxidation system

A new method for the determination of dye concentration based on photocatalytic oxidation digestion and spectrophotometry was established by using KMnO4 synergistic TiO2 photocatalytic oxidation and methyl orange solution as simulated dye wastewater. The mechanism of photocatalytic oxidation for the determination of dye concentration was discussed, and the optimal reaction conditions for dye digestion were investigated. The optimal digestion conditions were as follows: solution pH 1.5, TiO2 amount 1.0 g/L, KMnO4 initial concentration 10.0 mmol/L, solution temperature 80°C, ultraviolet light irradiation time 10 min. Compared with potassium dichromate reflux method or potassium permanganate method, the photocatalytic digestion method of TiO2-KMnO4 synergistic system is more rapid, efficient, economical and environmentally friendly, which provides a new idea for the determination of dye concentration in wastewater.

Effect of Different Radiation Sources and Noble Metal Doped onto TiO2 for Contaminants of Emerging Concern Removal

Water scarcity is a worldwide problem boosted by global warming and pollution of anthropogenic origin. The contaminants of emerging concern in water sources are increasing due to the inefficiency of conventional wastewater treatments, and these should be mitigated. Advanced oxidation processes appear as suitable solutions for decontamination. The photocatalytic oxidation of the mixture of sulfamethoxazole, carbamazepine and lorazepam was investigated. TiO2 modified by Ag and TiO2 modified by Pd were used as photocatalysts to improve photoactivity. The impact of light wavelengths was examined using UVA and visible radiation as well as natural sunlight. Visible light revealed the lowest ability for decontamination in 60 min of irradiation through Ag and Pd–TiO2 photocatalytic oxidation. On the other hand, UVA and sunlight in the presence of photocatalysts were able to totally remove the contaminants. This can be related to the high production of reactive oxidative species at those conditions. The increase of the noble metal load promotes the improvement of the decontamination efficiency. The kinetic rate was analyzed for UVA and sunlight radiation for different photocatalytic conditions. The presence of a natural light source without energy costs leads to an increase in the pseudo-first-order kinetic constant. Sunlight radiation with a suitable photocatalyst can be a very good option for water decontamination.

TiO2 photocatalytic degradation of the flame retardant tris (2-chloroethyl) phosphate (TCEP) in aqueous solution: A detailed kinetic and mechanistic study

The presence of halogenated organophosphate flame retardants in natural water systems is a widespread concern because of their potential threat to human health and the environment. TiO2 photocatalysis at 350 nm leads to rapid degradation of tris (2-chloroethyl) phosphate (TCEP). The observed degradation follows pseudo-first-order kinetics at a specific concentration. The apparent rate constants varied from 0.28 to 0.03 min−1 depending on the initial concentrations over the range of 18–270 μM, indicating the heterogeneous degradation process is likely controlled by mass transfer (adsorption↔desorption) at the surface of TiO2. The degradation kinetics also fit the Langmuir-Hinshelwood model with apparent kinetic parameters of 0.03 μM−1 and 13.1 μM min−1 for the apparent equilibrium constant (KLH) and the reactivity constant (krxn-LH) respectively. 1H- and 31P-NMR studies indicate sequential oxidation of the alkyl ester chains (alkyl phosphate), initially leading to the diester product, followed by the formation of the monoester and ultimately producing phosphate. Under strongly alkaline conditions the degradation is enhanced, from pH 4 to 9 the degradation is relatively constant, while under highly acidic conditions the degradation is inhibited. Effective mineralization is achieved as demonstrated by excellent chloride (98%) and phosphate (94%) mass balances as well as the loss of total organic carbon (TOC) >95%. The addition of an equal molar amount of the hydroxyl radical scavenger, coumarin, leads to pronounced reduction in degradation indicating hydroxyl radicals mediate the degradation process. These results demonstrate TiO2 photocatalytic oxidation has promise for the treatment of aqueous solutions contaminated with organophosphate flame retardants.

Immobilized chitosan-montmorillonite composite adsorbent and its photocatalytic regeneration for the removal of methyl orange

In this study, chitosan and clay-montmorillonite (CS-MT) composite was prepared and immobilized on glass plates for the removal of methyl orange (MO) dye from aqueous solution. The immobilized CS-MT was characterized using scanning electron microscopy-energy dispersive X-ray (SEM–EDX), Fourier transform infrared (FTIR), pore structural analysis and UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS). The addition of MT into the CS matrix produced a heterogeneous surface and slightly increased the surface area of the composite film. The adsorption study revealed that the pseudo-second-order kinetic and Langmuir isotherm models could well describe the adsorption of MO dye onto the immobilized CS-MT. After saturation, the spent CS-MT was regenerated via the TiO2 photocatalytic oxidation under UV–Vis irradiation. During the regeneration, the spent CS-MT underwent two concurrent processes: desorption of MO dye and photocatalytic oxidation of desorbed dye by the TiO2 photocatalyst. The photocatalytic regeneration of the spent immobilized CS-MT was highly effective in ultra-pure water at pH 11, as it mineralized up to 86% of the desorbed MO within 20 h of regeneration time.

Low-temperature activation of carbon black by selective photocatalytic oxidation.

Carbon black is chemically modified by selective photocatalytic oxidation, removing amorphous carbon and functionalizing the graphitic fraction to produce porous, graphitized carbon black, commonly used as an adsorbent in chromatography. In contrast to pyrolytic treatments, this photocatalytic modification proceeds under mild reaction conditions using oxygen, nitric oxide, water vapor and a titanium dioxide photocatalyst at 150 °C. The photo-oxidation can be performed both with the photocatalyst in close proximity (contact mode) or physically separated from the carbon. Structural analysis of remotely photo-oxidized carbon black reveals increased hydrophilic properties as compared to pyrolysis at 700 °C in a N2 atmosphere. Carbon black photo-oxidation selectively mineralizes sp3-hybridized carbon, leading to enhanced graphitization. This results in an overall improved structural ordering by enriching carbon black with sp2-hybridized graphitic carbon showing decreased interplanar distance, accompanied by a twofold increase in the specific surface area. In addition, the photo-oxidized material is activated by the presence of oxygen functionalities on the graphitic carbon fraction, further enhancing the adsorptive properties.

Removing Humic Acid from Aqueous Solution Using Titanium Dioxide: A Review

Recently, the photocatalytic degradation technique with titanium dioxide (TiO2) has been widely applied for the degradation of humic acid (HA) from aqueous solution due to its ability to achieve complete mineralization of organic contaminants. Because TiO2 is the most commonly used semiconductor photocatalyst, efforts on the modification of TiO2 in order to improve catalyst efficiency were presented in this review manuscript. The key photoreactor operation parameters such as TiO2 loading, pH, temperature, oxygen concentration, concentration and nature of HA, light wavelength, light intensity, the presence of inorganic ions and mechanistic pathway for pollutant removal, and the formation of the intermediates and their effects on the mineralization and disinfection of the photo- process were also assessed. Although we can see an increase in the number of papers that have been published in this area, further progress is needed to improve the understanding of the dynamic interactions between TiO2 photocatalytic oxidation process and HA, as well as to suggest possible future developments in this promising field.

Immobilized titanium dioxide/powdered activated carbon system for the photocatalytic adsorptive removal of phenol

Titanium dioxide (TiO2) and powdered activated carbon (PAC) were fabricated via a layer by layer arrangement on a glass plate using a dip-coating technique for the photocatalytic-adsorptive removal of phenol. Thinner TiO2 layer coated on PAC sub-layer has larger surface area and better phenol removal than the thicker TiO2 layer. The system obeyed the Langmuir isotherm model, which exhibited a homogeneous and monolayer adsorption with a maximum capacity of 27.8 mg g-1. The intra-particle diffusion was the rate-limiting step as the linear plot crossed the origin, while the adsorption was unfavorable at elevated temperature. Under light irradiation, the TiO2/PAC system removed phenol two-times more effectively than the TiO2 monolayer due to the synergistic effect of photocatalysis by TiO2 top layer and adsorption by PAC sub-layer. The COD removal of phenol was rapid for 10mg L-1 of concentration and under solar light irradiation. It was shown that the PAC sub-layer plays a significant role in the total removal of phenol by providing the adsorption sites and slowing down the recombination rate of charge carriers to improve the TiO2 photocatalytic oxidation performance.

TiO2 photocatalytic oxidation of a mixture of emerging contaminants: A kinetic study independent of radiation absorption based on the direct-indirect model

TiO2 photocatalytic oxidation of a mixture of four pharmaceutical emerging contaminants (ECs): caffeine, flumequine, ibuprofen and carbamazepine, has been studied both in ultrapure and municipal wastewater with the main aim of checking the direct and indirect transfer mechanism of this process. Also, given the high importance of knowing the volumetric rate of photon absorption (VRPA) for the kinetics of the process, actinometrical results have been compared to those from the six flux model (SFM) application. Finally, kinetic equations derived from the direct and indirect transfer mechanism of photocatalytic oxidation have been deduced to fit experimental results and conclude about the possible removal way of ECs in water when this advanced oxidation process is applied.

Using Photocatalytic Oxidation and Analytic Techniques To Remediate Lab Wastewater Containing Methanol

This experiment is dedicated to second-year and above undergraduates who are in their experimental session of the analytical chemistry course. Grouped students are required to use a TiO2 photocatalytic oxidation process to treat the methanol-containing wastewater that resulted from their previous HPLC experiments. Students learn to assemble a specified apparatus for a chemical reaction and analytical methods for the determination of environmental pollutants and reaction intermediates. The comprehensive experiment can give students a deep insight into application of several instruments (COD analyzer, UV–vis, GC-FID, and GC–MS) and the principle of photocatalytic oxidation reaction. Meanwhile, upon the completion of the experiment, students not only become aware of the wastes they generate but also understand how chemistry can be utilized for environmental remediation.

TiO2 crystal facet-dependent antimony adsorption and photocatalytic oxidation

Anatase TiO2 crystal facets are garnering increasing attention due to their unique surface property. However, no specific linear relationship had been derived between the facet exposed on TiO2 and the surface adsorption capacity as well as photocatalytic performance. This study systematically explored the facet effects on antimony (Sb) adsorption and photocatalytic oxidation using high-index {201} and low-index {101}, {001}, and {100} TiO2. The results suggest that high-index {201} TiO2 exhibits the best Sb(III) adsorption and photocatalytic activity compared to the low-index TiO2. Both the Sb(III) adsorption density and the amount of OH and O2− generated in solution were correlated to the magnitude of surface energy on TiO2 facets. Photocatalytically generated OH and O2− were responsible for Sb(III) photooxidation as evidenced by radical-trapping experiments. The great contribution of OH was observed only on {201}, not on low-index TiO2. This phenomenon was found to be attributable to the high surface energy on {201}, which enables the generation of a large amount of photogeneration OH to compensate for the fast rate of OH dissipation. Therefore, the predominant participation of OH in Sb(III) photooxidation was only possible on high-index {201} TiO2, which resulted in an enhanced photocatalytic rate. On the other hand, O2− dominated the Sb(III) photocatalytic oxidation on low-index TiO2. The intrinsic facet-dependent adsorption and photocatalytic mechanism obtained from this study would be useful for developing TiO2-based environmental technologies.

Appraisal of a hybrid air cleaning process.

Nowadays, there is an amplified interest in maintaining suitable indoor air quality (IAQ). Besides a wide range of available interventions, air cleaners are considered a valuable tool, since based on inexpensive and easily implementing technologies to improve IAQ. The purpose of this work is to combine the TiO2-photocatalysis with the electrostatic and adsorption processes, in order to improve efficiency and reliability. A TiO2-photocatalytic oxidation combined with an electrostatic filter has been studied. Nitrogen oxides reduction and degradation of many VOC over different catalyst support were monitored jointly with CO and CO2 production. The coupling of photocatalysis with an external electric field enhances efficiency of the process. The choice of materials with diversified adsorptive characteristics plays an important role in the durability of the process over time.

Dye-sensitized TiO2-catalyzed photodegradation of sulfamethoxazole under blue or yellow light.

Visible light-induced photocatalysis is potentially advantageous and could be an efficient approach to degrade contaminants because it can be used to selectively target specific wavelength for decomposition of organic contaminants in water and wastewater. This study demonstrates the photodegradation of sulfamethoxazole (SMX) using [Pt(3,3'-dicarboxy-2,2'-bpy)(1,2-benzenedithiolate)] (Complex 1)-sensitized and [Pt(4,4'-dicarboxy-2,2'-bpy)(1,2-benzenedithiolate)] (Complex 2)-sensitized titanium dioxide (TiO2) under blue or yellow light (420 or 580nm, respectively) irradiation in water. The Complex 1-sensitized TiO2 photocatalytic oxidation of SMX reached almost 100% removal under 420nm irradiation for 3h in water. In addition, the formation of hydroxyl radicals can be facilitated by bubbling O2 during the photodegradation in which an effective decomposition of SMX was observed. Based on HPLC and UV-Vis studies of the decomposed products, it was found that SMX underwent cleavage of aromatic rings during the photodegradation process.

Comprehensive study on effects of water matrices on removal of pharmaceuticals by three different kinds of advanced oxidation processes

Simple semi-theoretical models were developed to estimate the performance of three different kinds of advanced oxidation processes (AOPs) in the degradation of pharmaceuticals. The AOPs included the photo-Fenton process as an example of a liquid-liquid reaction, the TiO2 photocatalytic oxidation process as a solid-liquid reaction, and the combined ozone and hydrogen peroxide oxidation process as a gas-liquid reaction; the effects of the aqueous matrices (CESs: co-existing substances) of actual wastewater on the removal of pharmaceuticals (carbamazepine and diclofenac) was taken into account. By comparing the characteristic parameters of the models, obtained from the experiments using pure water and actual wastewater, the effects of CESs on the respective removal mechanisms could be separately and quantitatively evaluated. As a general tendency, the AOPs proceeded less effectively (were inhibited) in the matrices containing CESs, as observed with the use of a lower initial concentration of pharmaceuticals. The inhibition mechanisms differed for the three types of AOPs. In the photo-Fenton process, the Fenton reaction was improved by the incorporation of CESs, while the photo-reduction reaction was significantly inhibited. In the TiO2 photocatalytic oxidation process, competition between the pharmaceuticals and CESs for adsorption on the catalyst surface was a less significant inhibitory factor than the scavenger effects of the CESs. The combined ozone and hydrogen peroxide oxidation process was most strongly inhibited by CESs among the AOPs investigated in this study.