VOC Degradation Research Articles

Promotion effect of strong metal-support interaction to thermocatalytic, photocatalytic, and photothermocatalytic oxidation of toluene on Pt/SrTiO3

The importance of strong metal-support interaction (SMSI) in reducible oxide supported noble metal nanoparticles (NP) has been recognized in many thermocatalytic systems but rarely explored in photocatalytic and photothermocatalytic systems. Herein, the promotion effect of SMSI in strontium titanate (STO) supported Pt NP for thermocatalytic, photocatalytic, and photothermocatalytic oxidation (TCO, PCO and PTO) of toluene is reported. SMSI in Pt/STO is achieved through calcination in air (Air-Pt/STO), reduction in H2 atmosphere (H2–Pt/STO), wet reduction in HCHO solution (HCHO–Pt/STO) or NaBH4 solutions (NaBH4–Pt/STO), resulting in the formation of chemisorbed oxygen and negatively charged Pt NP and promoting oxygen activation in TCO and surface plasmon resonance effects of Pt NP in visible-light-induced PCO and PTO. Both TCO and PCO activities go along with the degree of SMSI as Air-Pt/STO > H2–Pt/STO > HCHO–Pt/STO > NaBH4–Pt/STO. Under both visible-light illuminating and thermal environment at 150 °C, the PTO toluene degradation efficiency of Air-Pt/STO is further improved with a factor of 32 times or 9 times than the single PCO or TCO process. The unique synergistic photothermocatalytic oxidation performance of Air-Pt/STO is ascribed to the function of Pt NP and the effect of SMSI. Our findings provide a facile way to design multifunctional supported noble metal catalysts for efficient VOCs degradation process.

Metal organic framework derivative-TiO2 composite as efficient and durable photocatalyst for the degradation of toluene

In this paper, the TiO2 catalyst is successfully modified with a metal organic framework derivative, N-doped graphite carbon (GC-N), by pyrolyzing ZIF-8 using a hydrothermal method. The resulting GC-N-TiO2 catalyst displays significantly improved performance in the photocatalytic degradation of toluene compared with Pt catalyst. In addition, the material exhibited high durability with stable performance after 20 recycles in static conditions and after 24 h of continuous use in dynamic conditions. The superior performance was attributed to the high conductivity and chemical stability of the catalyst. Also, the rich pyridinic N in GC-N facilitates the transfer of photogenerated electrons to oxygen, thereby promoting the generation of reactive oxygen species (ROS). This work provides new insight into the application of metal organic framework derivatives as a possible alternative to noble metal loaded materials in photocatalytic degradation of VOCs.

Gas-phase aromatic compounds degradation by a partially TiO2 coated photoreactor assisted with ozone

Heterogeneous photocatalysis with TiO2 have been studied for VOCs degradation; however, aromatic VOCs degradation lead TiO2 deactivation. The objective of this study was to degrade aromatic VOCs by heterogeneous photocatalysis avoiding TiO2 deactivation. The experiments were conducted using a UV-C lamp (254nm), relatively humidity (RH – 26–60 %), and ozone (O3 – 2.38 to 5.35 %). Due to O3 addition, it was necessary to have uncoated regions in the quartz tube around the lamp to allow UV photons to reach the gas bulk and generate radicals from O3. Different quartz tube coating fractions were tested to analyze its influence on VOCs degradation. The highest toluene degradation was 99.2 % for the reactor with 90 % of coating, 3.4 % of O3, space time of 123s, and RH of 26 %. It was observed RH greater than 26 % affected the degradation achieved. Ozone addition allowed TiO2 use for 77h avoiding early catalyst deactivation. Besides that, the requirement of uncoated regions indicated that VOC oxidative reactions occur both on solid and gas phases. This suggested that the addition of O3 combined with the reactor configuration is a promising alternative for aromatic compound degradation by heterogeneous photocatalysis.

Progress in degradation of volatile organic compounds based on low‐temperature plasma technology

AbstractOn the basis of plasma technology, the progress of the volatile organic compounds' (VOCs') degradation by low‐temperature plasma alone is discussed first, including reactor types, influencing factors of plasma degradation of VOCs and the reaction mechanism between plasma and VOCs. Then, the research status of three VOC degradation technologies (catalysis, adsorption, and biotechnology) and their synergistic degradation of VOCs with plasma are reviewed, including the effect of catalyst position on VOC degradation, the interaction mechanism between plasma and catalyst; the factors affecting the adsorption of VOCs by carbon‐based adsorbents and zeolite, the degradation of VOCs by plasma‐assisted adsorbent; the features of different biological systems, the influencing factors of VOC degradation by the biotrickling system, and the degradation of VOCs by plasma‐assisted biotreatment. Finally, the prospects of developments in high‐tech based on plasma are discussed.

Integrated adsorption and photocatalytic degradation of VOCs using a TiO2/diatomite composite: effects of relative humidity and reaction atmosphere

The optimal relative humidity condition for VOC degradation is related to the length of the carbon chain of VOCs.

Evaluation procedure of photocatalysts for VOCs degradation from the view of density functional theory calculations: g-C3N4 dots/graphene as an example

Various techniques have been utilized in experiments to evaluate the performance of photocatalysts and to understand the corresponding catalytic mechanism.

Isolated Pt single atomic sites anchored on nanoporous TiO2 film for highly efficient photocatalytic degradation of low concentration toluene

Single atom catalysts with atomically distributed active metal centers have attracted great attention owing to their maximum atom efficiency and excellent activity. Herein, we report a novel photocatalyst with isolated Pt single atomic sites anchored on nanoporous TiO2 film prepared by a facile immersion and reduction method. HAADF-STEM, XPS, XANES and EXAFS results confirmed the anchoring of Pt single atomic sites on nanoporous TiO2 film. The effects of immersion concentration of Pt, reduction temperature, relative humidity, inlet toluene concentration and residence time on photocatalytic degradation of low concentration toluene under UV and VUV irradiation were investigated. The results showed that the as-prepared catalyst had considerably high photocatalytic activity. The removal rate of toluene reached 45.88% under VUV irradiation when the inlet toluene concentration and residence time were 200 ppb and 0.3 s, respectively, which was 5.94 times that of pristine nanoporous TiO2 film. The by-product ozone removal was greatly improved and the corresponding energy consumption was 0.01 kW·h/m3. While the removal rate of toluene increased with the decrease of inlet toluene concentration under UV irradiation. The Pt single atom catalyst exhibits significant potential for photocatalytic degradation of low concentration VOCs in indoor environments.

Electroluminescence analysis of VOC degradation of individual subcell in GaInP/GaAs/Ge space solar cells irradiated by 1.0 MeV electrons

The open-circuit voltage (VOC) degradation for individual subcell in 1.0 MeV electrons-irradiated GaInP/GaAs/Ge solar cells has been analyzed using electroluminescence (EL) measurements. By using the relationship between VOC degradation and electron fluence, the capture cross section of the defects induced by electron irradiation in individual subcells were determined. Furthermore, by comparing the thermal activation energy and capture cross section, a defect located at Ev+0.55 ​eV styled H2 hole trap is nonradiative recombination centre in GaInP subcell, a defect located at EC-0.96 eV styled E5 electron trap is nonradiative recombination centre in GaAs subcell, and a defect located at EC-0.38 eV styled E-center electron trap is nonradiative recombination centre in Ge subcell.

Investigation of promotion effect of Cu doped MnO2 catalysts on ketone-type VOCs degradation in a one-stage plasma-catalysis system

Acetone and methyl ethyl ketone are two typical ketone-type VOCs which are commonly used as solvent in manufacturing factories. Their removal under plasma-catalysis over Cu-doped MnO2 catalysts were carried out in a coaxial dielectric barrier discharge (DBD) reactor in this study. The effects of Cu doping on the removal efficiency and CO2 selectivity of two ketone-type VOCs in this system are deeply investigated and compared as a function of specific energy density (SED). Experimental results show that the introduction of the Cu-doped MnO2 catalysts significantly enhances the VOCs removal performance and CO2 selectivity. Among them, Cu0.133Mn presents the highest removal efficiency (97% for methyl ethyl ketone and 82.1% for acetone) and the best CO2 selectivity (91.7% for methyl ethyl ketone and 89.4% for acetone) at the SED of ~600 J L−1 and a high GHSV of 300,000 mL·(g·h)−1. Based on the structure-function analysis of catalysts, it is believed that the synergistic effect between Cu and Mn in Cu-Mn solid solution can promote the amount of surface active oxygen and reducibility to improve catalytic performance. Furthermore, with the help of in situ FTIR and GC–MS, it is found that Cu-doped MnO2 catalysts can not only accelerate the VOCs degradation rate but also improve the oxygen and ozone utilization for VOCs complete oxidation. Besides, the possible degradation pathways of two ketone-type VOCs under the plasma and plasma-catalysis process have also been suggested and discussed at last.

Photocatalytic Degradation of Different VOCs in the Gas-Phase over TiO2 Thin Films Prepared by Ultrasonic Spray Pyrolysis

In this study, we deposited TiO2 thin films onto borosilicate glass by ultrasonic spray pyrolysis at 350 and 450 °C. The aim of study is to determine the effect of deposition temperature on photocatalytic activity of TiO2 thin films and to investigate the performance of TiO2 thin films on photocatalytic degradation of methyl tert-butyl ether (MTBE), acetone, acetaldehyde, and heptane as functions of different operating parameters. TiO2 thin films deposited at 350 and 450 °C have a thickness value of 190 and 330 nm, respectively. All as-prepared TiO2 films possess an anatase crystalline structure. According to the X-ray photon spectroscopy (XPS) study, the TiO2 thin film deposited at 350 °C showed a higher amount of oxygen vacancies and hydroxyl groups on the film surface after UV treatment. The aged-TiO2 thin film deposited at 350 °C showed a water contact angle (WCA) value of 0° after 10 min UV irradiation, showing superhydrophilic surface behavior. The TiO2 film deposited at 350 °C exhibited the highest amount of conversion of MTBE (100%). The results also showed that TiO2 films are capable of photocatalytic degradation of MTBE (100%) and acetaldehyde (approx. 80%) in humid air conditions and high airflow rate. The visible-light-activity of TiO2 thin films was tested with 5 ppm MTBE and acetone. TiO2 thin films deposited at 350 °C with a surface area of 600 cm2 showed 60% of MTBE and 33% of acetone degradation under VIS light.

Simultaneous degradation of n-hexane and production of biosurfactants by Pseudomonas sp. strain NEE2 isolated from oil-contaminated soils.

The presence of surfactants in biofilters could enhance hydrophobic VOC removal. In this study, blood agar plate, methylene blue agar plate and a culture with n-hexane as the only carbon source were used to screen strains that could biodegrade n-hexane and produce biosurfactants simultaneously. The effects of n-hexane concentration on n-hexane removal and biosurfactant production were also investigated. Results showed that such a strain identified to be Pseudomonas sp. Strain NEE2 was successfully isolated from oil-polluted soils. The biosurfactants production by this strain were dependent on the initial concentration of n-hexane (132-2640 mg/L). At the concentration of 2640 mg/L of n-hexane, the biosurfactants promoted n-hexane removal. At 132 mg/L of n-hexane, n-hexane removal efficiency on day 2 exceeded 60%. The synergistic mechanisms of n-hexane removal and biosurfactant production by Pseudomonas sp. Strain NEE2 were discussed including the enhanced mass transfer from gas to liquid phase, within the biofilm phase and biodegradation at the presence of biosurfactants as well as the consequently enhanced production of the biosurfactants. These results in this study proved that it is possible for microorganisms utilizing the synergistic effect of hydrophobic VOC degradation and biosurfactant production for cost-effective hydrophobic VOC removal in biofilters.

Plate-like WO3 inserting into I-deficient BiO1.2I0.6 microsphere for highly efficient photocatalytic degradation of VOCs

Abstract The key to photocatalytic efficient decomposition of VOCs is to significantly improve carrier separation-efficiency of the photocatalyst. Herein, we synthesized a novel photocatalytic composite material of I-deficient BiO1.2I0.6/WO3 by solvothermal method coupling with thermal decomposition. The PL spectrum and photoelectrochemical tests found that WO3 compounded by 40 wt% BiO1.2I0.6 greatly promoted its separation efficiency of carriers. This was mainly caused by the potential difference of band edge between the 40 wt% BiO1.2I0.6 and WO3 driving reverse shift of carriers in their space charge-layer. The 40 wt% BiO1.2I0.6/WO3 achieved 58.8% mineralization ratio in the process of degrading typical VOCs, toluene after 8 h irradiation, which was 15.9 and 2 times those of BiO1.2I0.6 and WO3, respectively. Gaussian calculation and ESR investigation demonstrated that toluene was decomposed by h+ and hydroxyl radical (·OH) under irradiation.

Electrochemically self-doped WO3/TiO2 nanotubes for photocatalytic degradation of volatile organic compounds

In this study, an electrochemically self-doped WO3/TiO2 nanotubes (R-WO3/TNTs) composite film was developed for the photocatalytic degradation of waste gas. The doping of oxygen vacancies (OVs) into the heterojunction of WO3/TNTs was conducted by a simple electrochemical approach, by which the quantity and distribution of OVs on surface as well as bulk were tailored with respect to the applied cathodic potential and the duration of the treatment. With an increase of applied cathodic potential as well as the duration, the quantity of OVs on WO3/TNTs was observed to be consistently raised, while those presented in the surface were raised initially and further showed a plateau trend as the duration extended at a fixed potential. The incorporation of OVs into WO3/TNTs enhanced the charge-transport resistance and reduced the electron-hole recombination, thereby showed an enhanced photocatalytic performance. The R-WO3/TNTs prepared by the electrochemical polarization process at −1.4 V (vs SCE) exhibited a 12 times higher photo-current density and obviously, an enhanced efficiency in the photocatalytic degradation of VOCs with a prolonging photostability compared to that of the pristine WO3/TNTs, under a simulated solar light irradiation. The single-time purification trial demonstrated the effectiveness of the R-WO3/TNTs composite in treating the VOCs for the practical application.

Photocatalytic indoor/outdoor air treatment and bacterial inactivation on CuxO/TiO2 prepared by HiPIMS on polyester cloth under low intensity visible light

In this study, photoactive CuxO/TiO2 coatings were prepared using magnetron sputtering operated at different powers and modes (Direct-current magnetron sputtering and High Power Impulse magnetron sputtering). Indoor/outdoor air pollutions (Volatile Organic Compounds, VOCs) degradation have been dramatically reduced on sputtered CuxO/TiO2 on polyester (PES) cloth under low intensity visible light. The Low intensity visible light was used to irradiate the sputtered photocatalysts, which degraded various VOC molecules concomitant with a bacterial inactivation ability. The VOC removal kinetics were studied in the dark and under visible light as a function of the deposition time and applied peak currents during the coating by HiPIMS. High concentrations of chloroform and butyraldehyde were shown to be degraded (90% and 85%, respectively) on CuxO/TiO2-PES fabrics under daylight irradiation. The repetitive reuse of the sputtered coatings was also investigated showing the long operational lifetime of the prepared fabrics. The deposition rates of Ti and Cu atoms and their atomic distribution along the sputtered film have been investigated by Transmission Electronic Microscopy (TEM). Redox catalysis was shown to happen within the VOC degradation time as detected by X-ray Photoelectron Spectroscopy (XPS). Deconvolution of the Cu2p3/2 peak in the CuxO/TiO2 on PES samples showed changes in the Cu2O and CuO within the VOCs degradation and the bacterial inactivation. The interfacial charge transfer (IFCT) between CuxO induced under light leading to VOCs oxidation path seemed to require a low photons energy and were able to oxidize the pollutants even at high concentrations. The mechanisms involving the VOCs degradation on CuxO/TiO2 catalysts are suggested in which the holes generated by Cu2O transfer to TiO2 in the TiO2(n)/CuxO(p) in the hetero-junction. This transfer is favored by the electrostatic interaction between both semiconductors. The photo-generated ROS, mainly ⦁OH-radicals were determined by fluorescence method. The possible contribution of the ⦁OH-radicals in the bacterial inactivation on the sputtered CuxO/TiO2 catalysts was discussed. DRS, TEM, contact angle (CA) and XPS were used to characterize the catalyst optical and structural properties.

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.

A Whole Cell Bioelectrochemical Sensor for the Monitoring of Benzene in Water

Bioelectrochemical Systems (BES) are a novel technology in which microorganisms degrade the organic matter in anaerobic conditions by using an electrode (anode) as final electron acceptor. Therefore, BES can be used as an effective strategy in environments where the absence of suitable electron acceptors limits classic bioremediation. Researches in progress demonstrated the possibility of apply innovative microbial electrochemical technologies for the monitoring and recovering of low concentration of organics, metals and micronutrients from polluted water environments, out of the electric grid. Recently BES have been also studied to stimulate the anaerobic degradation of hydrocarbons [1,2]. Although bioremediation is often inexpensive compared to physical-chemical methods, it typically requires more time and it is currently applied to a limited variety of pollutants. Benzene is a very toxic hydrocarbon and the pollution of this compound in fresh and groundwater causes many health and environmental problems. By monitoring the current produced by a BES, the rate of specific metabolic processes and the substrate concentration can be quantified in real time. The aim of this work is to study the correlation between the current produced in a BES and the concentration of benzene, in the rage of 10–60 mg/L. Tests were performed in single cell membraneless bioelectrochemical systems. The first run consisted in the inoculation of a BES with a refinery waste water in order to colonize the anode with an electroactive benzene-degrading bacterial community. Benzene was periodically supplemented to select a community able to degrade benzene. Current and benzene concentration were monitored, in order to correlate these parameters with the development of an electroactive biofilm. The application of this technology as biosensor for the monitoring of toxic compounds in water presents several advantages: low operational cost, versatility and the possibility to monitor in real time the concentration of pollutants from the environment. [1] M. Daghio, A. Espinoza Tofalos, B. Leoni, P. Cristiani, M. Papacchini, E. Jalilnejad, G. Bestetti, A. Franzetti. Bioelectrochemical BTEX removal at different voltages: assessment of the degradation and characterization of the microbial communities. Journal of Hazardous Materials, Volume 341, 5 November 2018, Pages 120-127 [2] S. Zhanga, J.Youa, C. Kennes, Z. Cheng, J. Ye, D. Chen, J. Chen, L. Wang. Current advances of VOCs degradation by bioelectrochemical systems: A review. Chemical Engineering Journal, Volume 334, 15 February 2018, Pages 2625-2637

Local Corrosion of Silicon as Root Cause for Potential‐Induced Degradation at the Rear Side of Bifacial PERC Solar Cells

Industrial bifacial PERC solar cells are exposed to a high‐voltage stress at the rear side. The tested cells show a potential‐induced degradation (PID) in Voc and Isc. From a front side current–voltage measurement, a power loss of about 12%rel is observed, however, without a significant change in the fill factor. The degradation is traced back to micron‐sized hole‐shaped damages of the rear surface, which correlate with localized regions of increased recombination. A focused ion beam (FIB) cross‐section through a hole‐shaped damage is performed for subsequent transmission electron microscopy (TEM) and energy‐dispersive X‐ray spectroscopy (EDXS). EDXS shows an accumulation of Na, K, and Ca impurities in the cavity. Thus, it is assumed that corrosion of the Si surface occurs beneath the AlOx/SiNy passivation layer stack and is accompanied by the formation of a SiO2 layer.

Open circuit voltage recovery in GaAsSbN-based solar cells: Role of deep N-related radiative states

In this work we investigate the effect of rapid thermal annealing (RTA) on the performance of solar cells consisting of different GaAsSbN-based structures and correlate the device results with modifications of the optical and structural properties of the alloy. In particular, bulk layers grown at different growth rates and type-II GaAsSb/GaAsN superlattices with different period thickness are analyzed. We find evidences of material quality improvement after the annealing process such as a reduction of N-related radiative defects and Sb clusters. These RTA-induced changes lead to a notable enhancement of the open circuit voltage (VOC), which results in values of the bandgap-voltage offset (WOC = EG/q-VOC) comparable to that of a non-optimized reference GaAs solar cell with the same device structure (WOC ∼0.63 eV). The decrease in WOC after annealing shows a correlation with the reduced radiative recombination at low energy N-related sub-bandgap states. These results suggest that radiative recombination in a broad band of deep defect states is a source of VOC degradation in GaAsSbN solar cells.

Integrated photocatalytic advanced oxidation system (TiO2/UV/O3/H2O2) for degradation of volatile organic compounds

Several advanced oxidation processes (AOPs) including photocatalytic processes were studied for effective treatment of complex model wastewater containing a wide variety of VOCs. The studies revealed synergistic effects of TiO2 based processes for improved degradation of the VOCs. A peroxone combined with TiO2/UV system (TiO2/UV/O3/H2O2) with a ratio between the oxygen source from the oxidant to chemical oxygen demand (COD) of the model wastewater (rox) of 0.5 and 100 mgTiO2/L was the optimal process. TiO2 revealed to be economically reasonable to be used in TiO2/UV/H2O2 and TiO2/UV/O3/H2O2 photocatalytic technologies for efficient and fast (100 min) degradation of VOCs with significantly low amounts of chemicals. Developed system provide high effectiveness with low treatment cost, which in case of most VOCs studied provide satisfactory effects in 15 min. of treatment process with 4 $/m3 of process costs. The technologies are promising in degradation and purification in several types of industrial effluents with a high VOCs content.

Promoting ring-opening efficiency for suppressing toxic intermediates during photocatalytic toluene degradation via surface oxygen vacancies

Aromatic ring-opening process is well recognized as the rate-determining step for catalytic toluene degradation. In photocatalytic toluene degradation, the toxic intermediates with harmful effects may be generated. To clarify the precise reaction mechanism and control the toxic intermediates generation, a closely combined in situ DRIFTS and DFT calculation is utilized to address these important issues. We construct the BiOCl with oxygen vacancies (OVs) and reveal the structure of OVs. The defect level caused by oxygen vacancies could promote the light adsorption and charge separation, which further boosts the activation of ring-opening species and enhances the generation process of free radicals. The reaction energy barriers of four possible ring-opening processes on defective BiOCl (OVBOC) are all declined in comparison with perfect BiOCl (BOC). The existence of oxygen vacancies could smooth the rate-determining step so the ring-opening efficiency of photocatalytic toluene degradation is highly increased. Most importantly, the methyl species would be further oxidized and tend to open the benzene-ring at benzoic acid on BOC while the ring would be broken at the benzyl alcohol on OVBOC. These results indicate that the toluene degradation pathway is shortened via the surface OVs, which enables the production of radicals with high oxidation capability for the accelerated chain scission of the ring-opening intermediates. Finally, the efficiency of the key ring-opening process could be enormously improved and toxic intermediates are effectively restrained. The present work could provide new insights into the design of high-performance photocatalysts for efficient and safe degradation of VOCs in air.