Ultraviolet Photocatalytic Oxidation Research Articles

The effect of ultraviolet photocatalytic oxidation on ferrocyanide electrochemical behavior—An important factor in mediator-based electrochemical sensors

The ferrocyanide/ferricyanide (‘fcn’) ion is a redox-coupled molecule used frequently as an analysis and validation analyte in electrochemical and optical measurements, due to its stability and reversibility features. However, currently there are no studies of how fcn’s electrochemical properties are affected by irradiation photocatalysis. In this work we present, for the first time, a shift in the electrochemical properties of a fcn couple by executing a continuous cyclic voltammetry test under the influence of multiple irradiation wavelengths (UV, blue, yellow, and brightfield). UV wavelength irradiation led to a significant shift in the half-wave potential (Ehalf), converging to a new steady state. We suggested a thermodynamic model including ferrocyanide, ferricyanide, and an electrochemically non-active pentacyanoaquaferrate to describe the change in electrochemical behavior. Enriching one’s knowledge of a fcn electrochemical response to irradiation photocatalysis is crucial for electrochemical-optical experiments and may suggest its use for a stable UV detection test.

Abatement of VOCs mixture of emerging concern by VUV-PCO process: From lab to pilot scale.

As a kind of emerging pollutant, volatile organic compounds (VOCs) are getting increasing attention due to their contribution to the formation of atmospheric haze and O3. Photocatalytic oxidation under vacuum ultraviolet photocatalytic oxidation (VUV-PCO) presents a promising method for VOCs degradation, but it is seldom studied for VOCs compound and the mechanism is still elusive. Herein, typical VOCs such as toluene and ethyl acetate were degraded separately or together in VUV system and in VUV-PCO system with the designed trifunctional catalyst Mn/TiO2/ZSM-5. Intermediates were recognized by PTR-TOF-MS. It is found that dual VOCs mixture outperformed single VOCs under both VUV process and VUV-PCO process. Possible degradation mechanisms were proposed. To explore the potential practicality of VUV-PCO technology, scale-up synthesis of Mn/TiO2/ZSM-5 on ceramic foams was successfully carried out and assembled into a homemade pilot-scale VUV-PCO equipment for the control of simulated VOCs complex (toluene, ethyl acetate, ethanol, and acetone). Pilot-scale catalytic testing with the monolithic catalysts achieved high removal efficiency (over 90 % efficiency after two cycles of regeneration) and confirmed the practical application possibility of VUV-PCO technology in multiple VOCs degradation. This work probes into the VUV-PCO technology applicability from lab scale to pilot scale and promotes the understanding of VUV and VUV-PCO in VOCs complex decomposition.

An efficient process for aromatic VOCs degradation: Combination of VUV photolysis and photocatalytic oxidation in a wet scrubber

The elimination of volatile organic compounds (VOCs) via vacuum ultraviolet (VUV) photolysis is greatly limited by low removal efficiency and gaseous byproducts generation, while photocatalytic oxidation of VOCs suffers from catalytic deactivation. Herein, a coupled process of gaseous VUV photolysis with aqueous photocatalytic oxidation with P25 as the catalyst was firstly proposed for efficient aromatic VOCs removal (VUV/P25). The removal efficiency of toluene reached 86.2% in VUV/P25 process, but was only 33.6% and 58.1% in alone gaseous VUV photolysis and aqueous ultraviolet photocatalytic oxidation (UV/P25) process, respectively. Correspondingly, the outlet CO2 concentration in VUV/P25 process reached 132 ppmv. Toluene was firstly destructed by high-energy photons generated from gaseous VUV photolysis, resulting in its incomplete oxidation to form soluble intermediates including acids, aldehydes, esters. These soluble intermediates would be further degraded and mineralized into CO2 in subsequent aqueous UV/P25 process. Notably, the concentrations of intermediates in VUV/P25 were much lower than those in VUV photolysis, indicating the synergy effect of VUV photolysis and UV/P25 process. The stability tests proved that VUV/P25 process maintained an excellent toluene degradation performance and P25 did not suffer from catalytic deactivation. In addition to toluene, the VUV/P25 system also achieved the efficient and sustainable degradation of styrene and chlorobenzene, suggesting its good application prospect in industrial VOCs treatment. This study proposes an efficient and promising strategy for deep oxidation of multiple aromatic VOCs in industries.

Evaluation of ozone removal devices applied in ventilation systems

Applying ozone removal devices in ventilation systems is an effective way to reduce building occupant exposure to ozone. However, little is known about the performance of commercially-available ozone removal devices under realistic usage conditions, especially for technologies that have recently emerged for general ventilation such as ultraviolet photocatalytic oxidation (UV–PCO) and catalysis (without UV). A total of 14 ozone removal devices that are representative of products on the market were selected: 11 activated carbon filters, 2 UV-PCO devices, and 1 catalyst filter without UV. We tested these devices with an “ozone stress test” by exposing them to 70 ppb, 107 ppb, and 500 ppb of ozone at 25 °C, 50% RH, and 2.5 m/s face velocity. The device performance was evaluated by the average efficiency at each ozone level, degradation rate at 500 ppb, pressure drop, and a quality factor that combines efficiency and pressure drop. Results show a wide range of single-pass removal efficiency from 3% to 93% at 70 ppb. All devices degraded at a slow rate; at 500 ppb, most devices degraded at 1.5%/h relative to their efficiency at the beginning of this period. The catalyst (no UV) and three 12″ activated carbon devices achieved high efficiency at the least cost of pressure drop. The loading and source of carbon had a significant impact on the efficiency of activated carbon filters. A two-fold increase in carbon loading led to nearly a two-fold higher single-pass removal efficiency. Coal-based carbon degraded 20 times faster than coconut shell-based carbon.

The research on the control of chlorinated by-products by the combined process of three-dimensional electrode system and ultraviolet-photocatalytic oxidation.

Advanced oxidation technology is considered to be the most potential wastewater treatment technology. As one of the advanced oxidation technologies, the three-dimensional electrochemical system (3DES) is often used to treat industrial wastewater that is difficult to degrade. Sulphonated phenolic resin (SMP) was treated as a characteristic pollutant in sulfonated drilling wastewater. The separate effect of current, the dosage of particle electrodes, chloride ion concentration and initial pH on chlorinated by-products were analyzed by response surface methodology (RSM). Results showed that current is the most dominant factor, followed by the dosage of particle electrodes. The ultraviolet-electrolysis (UVEL) system was implemented by adding ultraviolet light under the optimal electrolysis (EL) system. The chemical oxygen demand (CODcr) and total organic carbon (TOC) removal rates of the UVEL system were respectively increased by 19% and 29.39% compared with the EL system, the concentration of chlorinated by-products was also reduced by 534.4 mg/L when the UV irradiance was 5.24 mW/cm2. These results indicated that the UVEL system degrades SMP more thoroughly. The enhanced reaction mechanism of the UVEL system and the possible degradation pathway for SMP were proposed by controlling free radical quenching experiments and the product of EL and UVEL processes. The results showed that the high degradation efficiency of the UVEL system could be attributed to the synergistic degradation mechanism present in the UVEL system, where the photolysis of active chlorine species (ACl) promotes the increase of hydroxyl radical (·OH).

Experimental investigation on decomposition of ethylene by ozone: Harmful product, food safety, and control strategy

Ethylene not only causes food spoilage, but also reacts with ozone to form formaldehyde as a harmful intermediate byproduct. To assess the necessity of reducing formaldehyde formation and the use of air cleaning technologies, such as ultraviolet photocatalytic oxidation technology (UVPCO) or plasma, the formation rate of formaldehyde with different concentrations of ethylene and ozone under cold chain temperatures (1.67/14.00℃) is investigated comprehensively through an experimental study, and the adsorption of formaldehyde on apples and bananas is investigated as well. The results show that ethylene and ozone can react and produce formaldehyde up to 1 ppm under the conditions used in this study, and that formaldehyde can be adsorbed by fruits such as apples and bananas at a stable rate. Finally, two pilot tests are conducted to evaluate UVPCO and plasma technologies for ethylene removal; the results indicated that UVPCO and plasma can effectively remove ethylene. Novelty impact statement This work shows that ethylene and ozone can react and produce formaldehyde up to 1 ppm under the conducted condition in this paper, which can be adsorbed by fruits, such as apples and bananas at a stable rate. Finally, two pilot tests were conducted to evaluate UVPCO and plasma technologies for ethylene removal, and the results indicate that UVPCO and plasma can effectively remove ethylene.

Heterogeneous Photo-Fenton Catalytic Degradation of Practical Pharmaceutical Wastewater by Modified Attapulgite Supported Multi-Metal Oxides

Chemical synthetic pharmaceutical wastewater has characteristics of high concentration, high toxicity and poor biodegradability, so it is difficult to directly biodegrade. We used acid modified attapulgite (ATP) supported Fe-Mn-Cu polymetallic oxide as catalyst for multi-phase Fenton-like ultraviolet photocatalytic oxidation (photo-Fenton) treatment with actual chemical synthetic pharmaceutical wastewater as the treatment object. The results showed that at the initial pH of 2.0, light distance of 20 cm, and catalyst dosage and hydrogen peroxide concentration of 10.0 g/L and 0.5 mol/L respectively, the COD removal rate of wastewater reached 65% and BOD5/COD increased to 0.387 when the reaction lasted for 180 min. The results of gas chromatography-mass spectrometry (GC-MS) indicated that Fenton-like reaction with Fe-Mn-Cu@ATP had good catalytic potential and significant synergistic effect, and could remove almost all heterocycle compounds well. 3D-EEM (3D electron microscope) fluorescence spectra showed that the fluorescence intensity decreased significantly during catalytic degradation, and the UV humus-like and fulvic acid were effectively removed. The degradation efficiency of the nanocomposite only decreased by 5.8% after repeated use for 6 cycles. It seems appropriate to use this process as a pre-treatment for actual pharmaceutical wastewater to facilitate further biological treatment.

Modeling of photocatalytic oxidation reactor for methyl ethyl ketone removal from indoor environment: Systematic model development and validation

This paper describes the development of a model for predicting the performance of ultraviolet photocatalytic oxidation (UV-PCO) reactor for the removal of volatile organic compounds (VOCs) from indoor environment. The proposed model performance was validated at two stages. First, it was validated by comparing its performance with the prediction made by other models (inter-model comparison), and with experimental data from two different scales (pilot and bench) of UV-PCO reactors. A good agreement (with R2 = 0.98) between the developed model prediction and the experimental data was observed.Simulation of light intensity with linear source spherical emission model (LSSE) in bench-scale reactor showed a more uniform distribution than pilot-scale, due to longer distance of the lamp from the media in the bench-scale reactor. Beer-Lambert model demonstrated that light absorbed totally with one media, and adding extra media does not improve the PCO removal performance. Furthermore, Langmuir-Hinshelwood (L-H) rate expression by considering competitive effect of water and by-products with target compound was used. Formaldehyde and acetaldehyde were identified as the main by-products of the Methyl Ethyl Ketone (MEK) PCO reaction.A sensitivity analysis was performed to investigate the impact of three dimensionless parameters—Peclet (Pe), Stanton (St), and Damköhler (Da) numbers on the system performance. Simulation results indicated the UV-PCO process is mainly limited by the reaction rate at low removal efficiency. For higher removal efficiency, both the photochemical reaction rate and advective mass transfer have a significant impact on the system performance. The practical validation of the dimensionless model at two different scales of PCO reactor with same operating condition indicated that the proposed dimensionless model analysis can provide useful advice (qualitatively and quantitatively) for scale-up of PCO for the real application.

Mechanistic study of vacuum UV catalytic oxidation for toluene degradation over CeO2 nanorods

The present study specifically investigates vacuum ultraviolet (VUV) catalytic oxidation for toluene degradation over CeO2 nanorods. Synergetic effects of ultraviolet photocatalytic oxidation (UV-PCO) and ozone catalytic oxidation (OZCO) were manifested in the results of toluene removal and COx generation, while the combination of UV-PCO and OZCO (UV-OZCO) did not lead to improvement of mineralization. All the processes contribute to ozone decomposition, but no obvious synergetic effects of the different processes can be observed. Intermediate analysis results indicated that more toluene was oxidized into by-products, such as benzyl alcohol and benzaldehyde, by UV-OZCO rather than forming COx. Both hydroxyl radical (·OH) and superoxide radical (·O2−) were found in all the processes of the VUV-PCO-OZCO system (combination of VUV photolysis, UV-PCO, OZCO and UV-OZCO processes). In the UV-OZCO process, the formation of hydroxyl radical was promoted, while that of superoxide radical was impeded, resulting in lower mineralization level of toluene. The mechanistic study of toluene degradation over CeO2 nanorods in the VUV-PCO-OZCO system revealed that with the formation of ·O2− and ·OH, toluene is first oxidized to intermediates, followed by further ring–opening reaction and, finally, degradation into CO2 and H2O. CeO2 nanorods function as both ozonation catalyst and photocatalyst, and the redox pair of Ce3+ and Ce4+ are interconvertible and can keep a balance.

An improved numerical model of a UV-PCO reactor for air purification applications

Ultraviolet photocatalytic oxidation (UV-PCO) is a promising gaseous volatile organic compounds (VOCs) elimination method, of which the PCO kinetics are closely related to the radiation and airflow (contaminants) fields. Mathematical models have been developed in extensive studies to demonstrate the PCO kinetic reactions. Computational fluid dynamics (CFD) simulation was also carried out to display the irradiance and flow fields in the reactor. However, it still lacks an in-depth understanding of the light and mass transfer within the porous film coating where the microscopic structures dominate. To close this gap, this paper concentrates on the development of mathematical models for describing the light propagation, mass transfer, and reaction kinetics within the porous film coating. Incorporated with a CFD model for solving the mass, momentum and energy conservation, the sophisticated PCO process in the reactor can be accurately reproduced. The developed models have been validated by the experimental data, and are comparable with other models in the literature. The developed numerical models provide the implications of mass transfer for film coating UV-PCO reactor design.

Modeling of gas-phase heterogeneous photocatalytic oxidation reactor in the presence of mass transfer limitation and axial dispersion

Mass transfer plays a critical role in the efficiency of photocatalytic oxidation (PCO) technology for air purification applications. There has been limited work on the exploration of mass transfer in the PCO reactor with the non-ideal flow. In this work, the performance of a continuous heterogeneous ultraviolet photocatalytic oxidation (UV-PCO) reactor was investigated and addressed under mass transfer limitation and axial dispersion. First, CFD modeling was used to determine the flow distribution in the reactor at various airflow rates. The residence time distribution (RTD) analysis with a tracer gas (CO2) was carried out for the experimental validation of the simulation model and good agreement between experimental and simulation data was achieved. Further, a quick and straightforward methodology employing an axial dispersion plug flow model was used to study the RTD. The proposed model could predict the residence time distribution of CO2 with high accuracy. Results of the RTD for CO2 in the presence and absence of a PCO filter (silica fiber felts (SFF) modified with TiO2) were almost identical due to the high porosity of the filter. The model was then used for the evaluation of the axial dispersion of methyl ethyl ketone (MEK) at different flow rates. Owing to a low value of the Peclet number (Pe < 100), the flow in the reactor deviated from an ideal plug flow and dispersion could not be ignored. The photocatalysis reaction of MEK by the SFF filter under the mass-transfer-controlled regime was further addressed. A steady-state mass balance equation was implemented for the assessment of the performance of the UV-PCO reactor in the presence of axial dispersion and mass transfer limitation. The mass transfer coefficient was calculated with the use of the developed model and a correlation for the Sherwood number was proposed to relate the mass transfer coefficient to the flow rate and fiber structure. The proposed correlation was assessed and compared with the other empirical formulas available in the literature.

Removal of aqueous arsenite by simultaneous ultraviolet photocatalytic oxidation–coagulation of titanium salts: effect of precipitate particles size and solution chemistry

Removal of aqueous arsenite by simultaneous ultraviolet photocatalytic oxidation–coagulation of titanium salts: effect of precipitate particles size and solution chemistry

Numerical Simulation of a UV-PCO Plate Reactor

Ultraviolet photocatalytic oxidation (UV-PCO) system has gained increasing attention in indoor air treatments, of which the PCO reaction kinetics mainly depend on the radiation and airflow (contaminants) fields. It is recognized that the airflow rate has a significant influence on the PCO kinetics with the balance of the VOC mass transfer process. However, there are few discussion for the airflow rate dependency in the PCO kinetic reaction model. In addition, most of the studies in the literature assumed the incident surface irradiance was the energy participating in PCO reactions, which is not accurate. Hence, a 3D Computational Fluid Dynamics (CFD) model, including catalyst photon absorption coefficient, the conservation of mass, momentum, energy, and species, as well as PCO reaction kinetics, was introduced in this study. The determined model parameters were verified by the experimental data for a plate reactor challenged with 10 ppm acetone. The airflow rate dependency was examined in conjunction with CFD providing local flow field information, and the catalyst absorbed light intensity was quantified by a validated radiation model. It was found that the PCO removal efficiency predictions from the developed mathematical model agree with experimental data.

In-situ synthesis of heterojunction TiO2/MnO2 nanostructure with excellent performance in vacuum ultraviolet photocatalytic oxidation of toluene

A series of TiO2/MnO2 heterojunction catalysts were fabricated through an in-situ hydrothermal method, and for the first time, catalysts with this heterojunction structure were used for VUV-PCO toluene degradation. After the MnO2 coating, the TiO2/MnO2 catalysts performed excellently for both VOCs degradation and residual ozone decomposition with removal efficiency reaching 96.0% and 99.9%, respectively. The enhanced photocatalytic activity towards toluene degradation could be attributed to the heterojunction structure of TiO2/MnO2, which provides excellent contact between MnO2 and TiO2, and suppresses the recombination of photogenerated electron-hole pairs. Moreover, benefiting from the MnO2, the ozone generated in the system could be efficiently utilized and eliminated during the VUV-PCO process. The photocatalytic mechanism of TiO2/MnO2 for the toluene degradation and ozone decomposition was proposed.

Novel pseudo PMOS ultraviolet photo catalytic oxidation (PP-UVPCO) sensor for air purification

Novel pseudo PMOS ultraviolet photo catalytic oxidation (PP-UVPCO) sensor for air purification

Photocatalytic oxidation of volatile organic compounds for indoor environment applications: Three different scaled setups

Ultraviolet photocatalytic oxidation process (UV-PCO) is a promising approach for removing indoor volatile organic compound (VOC). Although the adequate efficiency of PCO in laboratory conditions has been proven, the application of PCO in VOCs degradation has been greatly hindered in large-scale applications. The effect of scaling up and real conditions cause some limitations for large-scale systems. Based on our knowledge, despite extensive published research on PCO of TiO2-based photocatalysts in bench-scale setups, there is a lack of studies regarding the effects of scaling up and by-product generation in pilot and full-scale setups. The main objective of this study is to investigate the scaling effect on toluene and isobutanol removal efficiency and by-product generation in conditions close to the real application. For this purpose, three test setups i.e., full, pilot, and bench-scale, were employed to investigate the PCO removal of VOC pollutants in the gas phase. Also, the effect of light type on the performance of PCO was examined in the pilot and full-scale. A brief description of three setups is presented, followed by experimental results and discussions about the difference between each setup. The PCO efficiency and by-product generation rate are evaluated in conditions close to the real application, considering low-level contaminant concentration, small residence time, and high flow rate. The relative humidity for all experiments is kept in the comfort zone (RH ∼50 ± 5%). The performance of vacuum UV (VUV) photolysis and VUV-PCO in pilot and full-scales, and UVC-PCO in all three scales, are compared and discussed.

Modeling of by-products from photocatalytic oxidation (PCO) indoor air purifiers: A case study of ethanol

Ultra-violet photocatalytic oxidation (UVPCO) technology has been receiving extensive attention for indoor air purification in recent two decades. However, the formation of by-products during the UV-PCO process darken its prospect of providing healthy indoor air quality (IAQ). This study examines by-product generation and operational parameters from 36 UV-PCO tests using a pilot duct system with the objectives of developing reliable by-product predictive models. The statistical analysis aimed at establishing linear and non-linear regression models to predict the concentrations of formaldehyde and acetaldehyde based on factors such as concentration, RH, airflow, and irradiance. The developed linear models provided satisfactory estimations of acetaldehyde and the sum of formaldehyde and acetaldehyde (FA) levels with regression coefficients (R2) of 0.74 and 0.84, respectively. Parametric study and bivariate analysis further confirm the statistical significance of independent variables on the acetaldehyde and FA productions. The PCO reaction pathway was proposed to explain that the presence of some strongly bounded intermediates on the surface decreased the reactivity of acetaldehyde to be further oxidized to formaldehyde.

Performance of an innovative VUV-PCO purifier with nanoporous TiO2 film for simultaneous elimination of VOCs and by-product ozone in indoor air

An innovative vacuum ultraviolet photocatalytic oxidation (VUV-PCO) air purifier, consisting of a photocatalytic unit bearing nanoporous TiO2 film, an ozone removal unit bearing Mn-Fe catalyst and a radial fan, was designed and constructed. The performance of the VUV-PCO air purifier in simultaneous elimination of VOCs and O3 by-product was, for the first time, evaluated in a sealed actual room. The evaluation was conducted in both intermittent on/off and continuous operations. The results illustrated that the air purifier had high efficiency in removing formaldehyde and moderate efficiency in removing benzene, toluene, ofm-xylene, ortho-xylene, pentanal, octanal and nonanal, which were released from particleboard into the sealed room. During the removal of formaldehyde decomposition and TVOC in intermittent three-time on/off operation, the air purifier exhibited good stability. During the operation without heating, the air purifier had high formaldehyde and TVOC removal efficiencies, reaching values of about 48.00% and 78.71%, respectively after 90 min. During the continuous operation, the air purifier was able to continuously and effectively remove formaldehyde, benzene homologues, aldehyde and ketone compounds, while the ozone removal unit was able to effectively eliminate ozone generated during VUV photocatalysis. The removal of TVOC by 38.25% was reached after 240 min. In addition, heating the ozone removal unit was found to not only accelerate the release of VOCs from particleboard, but also promote the decomposition of ozone. The ozone removal unit operated with heating was able to reduce ozone content from 250 to 75 ppb.

Photocatalytic degradation of VOCs on various commercial titanium dioxides: Impact of operating parameters on removal efficiency and by-products generation

Ultraviolet photocatalytic oxidation (UVPCO) is regarded as one of the promising technologies for indoor air remediation. The present study examines the photocatalytic activity of four commercialized titanium dioxide photocatalysts (P25, PC500, UV100, and S5-300A) in a small-scale single-pass continuous flow reactor. Challenge compounds have been chosen from two prevalent VOC families in indoor environment: toluene (aromatics) and methyl ethyl ketone (ketones). The influence of key experimental conditions including concentration (100–1000 ppb), relative humidity (0–50% at 23 °C), light intensity (1.25–5 W m−2), and residence time (0.02–0.1 s) on removal efficiency are evaluated. Due to the fact that one of the main shortcomings of PCO air purifiers is by-products generation, a special emphasis is put on identification and quantification of gaseous by-products using HPLC and GC-MS methods. The obtained efficiencies on various photocatalysts are explained considering crystalinity, crystalline phase, crystal size, surface area, and population of surface hydroxyl groups. Despite possessing lower crystalinity, PC500, UV100 and S5-300A outperformed P25 in toluene and MEK removal efficiency, primarily owed to their larger surface area, smaller crystal size, and higher concentration of surface hydroxyl groups. Acetone, acetaldehyde, and formaldehyde were identified as the main gaseous by-products in PCO of toluene and MEK.

Deactivation and ultraviolet C-induced regeneration of photocatalytic oxidation air filters

Ultra-violet photocatalytic oxidation has been regarded as one of the promising air purification technologies for improving indoor air quality. However, limited availability of experimental data in terms of photocatalyst deactivation and regeneration has hindered successful implementation of ultra-violet photocatalytic oxidation air cleaners in mechanical ventilation systems. The objective of this study is to obtain knowledge of the ultraviolet C-induced regeneration method, the simplest on-site approach, for the recovery of photocatalytic activity of photocatalytic oxidation filters after challenging ultra-violet photocatalytic oxidation systems with approximately 100 ppb of acetone or methyl ethyl ketone. Experimental observations of photocatalyst deactivation, and characterization of fresh and deactivated photocatalyst with the scanning electron microscope technique were presented. During the regeneration process, the production rates of formaldehyde, acetaldehyde, and acetone were hourly quantified under a short-term and a long-term ultraviolet C illumination. The regeneration performance was also examined and compared by testing the single-pass removal efficiency of regenerated photocatalytic oxidation filters by two methods: ultraviolet C illumination and O3-included ultraviolet C illumination. The results indicate that the ultraviolet C-induced regeneration method, superior to O3-assisted ultraviolet C method, plays a certain role in partial recovery of the photocatalytic activity. The degree of recovery would depend on the nature of contaminant gases previously processed in ultra-violet photocatalytic oxidation since different VOCs generate various types and amounts of surface adsorbed by-products, which resist regeneration at a different level.Graphical . UV-PCO represents a new generation technology for improving indoor air quality. However, little is known about photocatalyst deactivation and regeneration which is a major concern for the purpose of commercialization. The current objective is to explore the UVC-induced regeneration method, the simplest on-site approach, employed in an HVAC system. This work demonstrates a systematic evaluation of deactivation and UV-induced regeneration performance under the conditions relevant to the actual applications for two VOCs. In addition, the gaseous by-product generation rates and O3-assited UVC-induced recovery method were examined for the first time.