Photocatalytic Oxidation Process Research Articles

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.

Synergistic Performance between Visible-Light Photocatalysis and Thermocatalysis for VOCs Oxidation over Robust Ag/F-Codoped SrTiO3

Catalytic oxidation is an important removal route of volatile organic compounds (VOCs) pollution. Traditional thermocatalytic oxidation requires either expensive noble metal catalysts or a high reaction temperature, while most photocatalytic oxidation suffers from a low efficiency for the purification of high-concentration or refractory VOCs (e.g., aromatic compounds). Herein, we present an efficient visible-light-induced photothermocatalytic VOCs degradation way through constructing the fluorine ions and cheap Ag nanoparticles comodified SrTiO3 catalyst (Ag/F-STO). A photothermocatalytic synergistic effect is demonstrated on Ag/F-STO, providing a higher degradation efficiency than the contribution sum of photocatalytic oxidation and thermocatalytic oxidation. A higher toluene degradation rate constant than state-of-the-art photocatalytic toluene oxidation process and a (>) 95% conversion of benzene, toluene, and xylene mineralization are achieved on Ag/F-STO by photothermocatalysis at 90 °C upon visible ...

Fabrication of MoS2@g-C3N4 core-shell nanospheres for visible light photocatalytic degradation of toluene

The semiconductor-based photocatalytic oxidation process is considered as one of the most economical and environmentally friendly approach for the degradation of toluene. For the sake of exploring an efficient visible-light-driven photocatalysts, the MoS2@g-C3N4 core-shell nanospheres were successfully fabricated by taking the advantages of the morphology and structure of materials tailoring and semiconductor coupling, via a two-step approach including the hydrothermal method followed by ultrasonic adhering approach. The morphology, crystallinity, composition, and optical property of as-prepared catalysts were well characterized. The core-shell structure was fabricated by using MoS2 as the template and the coating of g-C3N4 improved the separation of photoinduced charges, due to the strong electronic interaction between them. The photocatalytic activity of MoS2@g-C3N4 core-shell nanospheres had been investigated by the degradation of toluene under visible light irradiation using in situ Fourier transform infrared (FTIR) spectroscopy. The MoS2@g-C3N4 nanospheres displayed enhanced visible-light photocatalytic activity, which is about 1.3 and 9.6 times than that of g-C3N4 and MoS2 nanospheres under identical conditions. Electron spin resonance (ESR) examinations confirmed the generation of ·OH and ·O2−, which were the key reactive oxygen species involved in the photocatalytic process.

Facile synthesis and characterization of a cobalt phthalocyanine sensitized SnIn4S8 composites toward enhanced photocatalytic activity

A series of cobalt phthalocyanine (CoTNPc)/SnIn4S8 composites with different mass proportions were prepared by ultrasonic method. The obtained composites have been characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectra diffuse reflection spectroscopy, Raman spectroscopy and photoluminescence. It was found that the photocatalytic performance of 10%-CoTNPc/SnIn4S8 composites was 3.18 times larger than that of bare SnIn4S8 under 100 min visible-light irradiation. More importantly, the 10%-CoTNPc/SnIn4S8 composites possessed the maximum photocatalytic activity whose degradation rate approached to around 99.2% and the cyclic experiment verified the stability of CoTNPc sensitized SnIn4S8 composites. In addition, some typical scavengers were added to speculate the potential photocatalytic mechanism during the photocatalytic oxidation process. This photocatalytic enhancement of CoTNPc/SnIn4S8 composites was attributed to its efficient charge transfer and inhibition of the recombination around electron–hole pairs.

Facile preparation of multi-doped TiO2/rGO cross-linked 3D aerogel (GaNF@TGA) nancomposite as an efficient visible-light activated catalyst for photocatalytic oxidation and detoxification of atrazine

The novel Ga, N, F co-doped TiO2@rGO aerogel (GaNF@TGA) nanocomposite was synthesized using a facile chemical method in the presence of ascorbic acid as a reducing agent and cross-linker. The XRD patterns indicated the lower intensity of the anatase XRD peak in doped-sample, which confirmed successful insertion of dopant atoms in the TiO2 lattice. FT-IR and Raman spectra confirmed the successful reduction of GO in the nanocomposite. The SEM and HRTEM images revealed the interconnected porous 3D network structure for the prepared TGA samples. Co-doping TiO2 with Ga, N and F caused considerable red shift in the absorption edge to the visible-light region. TGA catalyst had much higher photocatalytic activity than the plain TiO2 under visible-light irradiation due to the enhanced photogenerated charge separation for oxidation of atrazine (ATZ). The complete degradation of 40 mg/L ATZ was obtained in the photocatalytic oxidation process within 60 min with GaNF@TGA as catalyst. The reaction with OH at the surface of catalyst was the main mechanism contributed in degradation of ATZ in the developed photocatalytic process. The prepared catalyst showed a remarkable stability and simply separation for recycling. The cytotoxicity of fresh and photocatalytic-treated ATZ solutions assessed using the skin fibroblast cells (Hu02) indicated that treating ATZ solution in the developed visible-light photocatalytic reaction under optimum experimental conditions could considerably be detoxified. Accordingly, TGA is an efficient visible-light activated nanocomosite, which can be used as photocatalyts for enhanced degradation and detoxification of the emerging water contaminants.

Potential use of solar photocatalytic oxidation in removing emerging pharmaceuticals from wastewater: A pilot plant study

A pilot plant was used to evaluate the potential of solar photocatalytic processes in the treatment of wastewater containing emerging contaminates. Four groups of commonly used pharmaceuticals (antibiotics, estrogens, acidic, and neutral) were selected as model compounds and were treated with different combinations of solar advanced oxidation processes including solar-photolysis, homogenous solar oxidation with ferric ions, heterogeneous solar oxidation with titanium dioxide, and solar ozonation. Oxidation experiments were performed in Doha, Qatar (25.2854°N, 51.5310°E) under natural sunlight and at ambient temperature, in a semi-batch photo-reactor. Treatment performance was evaluated based on the efficiency of the processes in removing the target compounds and in mineralizing the organic content of the aqueous solution. The improvement in biodegradability and the reduction in the toxicity of the aqueous solution before and after the treatment were also evaluated. The results show that solar photolysis and solar oxidation with ferric ions are not effective in removing or mineralizing aqueous solutions containing the selected contaminates, while solar-driven oxidation processes with ferric ions, titanium dioxide, and ozone rapidly removed these pharmaceuticals from the wastewater and to some extent decreased the organic carbon content of the solutions. The removal efficiencies with solar photolysis and solar oxidation with ferric ions did not exceed 12.7% and 28.3%, respectively. Adding H2O2 to solar oxidation with ferric ions or utilizing TiO2 increased the percentage removal to the range 80–96%. Ozonation and solar ozonation processes removed 90–100% of the pharms in very short time. Performance indictor analysis showed that combining solar photocatalytic oxidation process with ozonation significantly improved the removal performance, increased the degree of mineralization, reduced the chemical requirements, and reduced the demand for ozone and energy. The kinetic profile of the combined processes is higher than that of the single oxidation process; thus, the combined oxidation processes is recommended for efficient treatment. The oxidation processes with their effective degradation capacity improved wastewater biodegradability and reduced its acute toxicity.

Mineralization of dichloromethane using solar-oxidation and activated TiO2: Pilot scale study

The oxidation of gaseous dichloromethane (DCM) by advanced oxidation technology, advanced solar oxidation technology, biological treatment, and the combination of solar advanced oxidation technology and biological treatment were investigated in a pilot study. The effects of the inlet concentration of DCM, flow rate, and relative humidity on the percentage DCM removal were recorded. Photolysis and photocatalytic oxidation using TiO2 does not result in the complete removal of DCM, while ozone, ozone/solar-hν and TiO2/ozone/solar-hν can completely remove DCM from the gas stream. Combined photocatalytic oxidation processes enhance the process efficiency and reduce both ozone demand and the energy requirements needed to completely remove DCM. Through a combination of processes, ozone, solar photons, and hydroxyl radicals oxidize DCM, generating byproducts that are water soluble and more biodegradable than the original DCM, providing the possibility for it to be combined with subsequent biological treatment. The decomposition of DCM was affected by the inlet flow rate, gas relative humidity, and gas flow rate with high percentage DCM removal achieved at low flow rate, DCM initial concentration up to 200 mg/m3, and humidity around 40%. The kinetics of DCM oxidation in different processes were successfully modeled to pseudo-first order or second-order kinetics. The kinetic analysis showed that the choice of oxidation process greatly affected the kinetic constants of DCM conversion, and RH 40% could cause faster oxidation. The results support the use of solar oxidation, not only for the mineralization of DCM, but also as a pretreatment before biodegradation.

Photocatalytic treatment of VOC industrial emissions: IPA removal using a sensor-instrumented reactor

This work aims at evaluating the applicability of photocatalytic oxidation (PCO) for industrial emission treatment. A dedicated single-pass semi-industrial PCO reactor is designed and the PCO removal of isopropanol (IPA) is investigated under industrial conditions: (i) high IPA concentrations ranging from 1.8 to 14.6 ppm and (ii) high air flow rates ranging from 26 to 146 m3.h−1. The concentrations of upstream and downstream IPA and by-products are monitored, not only using analytical instruments (mass spectrometry), but also gas micro-sensors. This approach aims at assessing the aptitude of commercially available micro-sensors to monitor a semi-industrial PCO reactor, and estimating their ability to automate such a process for industry. First, the influence of the main process parameters has been addressed: (i) IPA concentration, (ii) total air flow rate, (iii) number of PCO stages and (iv) number of PCO media. Irrespectively of the process condition, IPA PCO does not lead to deactivation of the media; whereas IPA mineralization and side-products formation are directly impacted by the process parameters. The increase of IPA concentration and air flow rate inhibits IPA mineralization, while the increase of number of stages and media promotes IPA mineralization. It is evidenced that selected gas micro-sensors can provide a semi-quantitative monitoring of the process performances. The main limitations of sensors are (i) their resolution regarding the detection of concentration variations and (ii) their cross-sensitivity to various classes of VOCs. Nevertheless, some sensors could be relevant for the automation and control of the PCO process once a preliminary metrological validation with relevant analytical devices is performed.

Effect of the wavelength on the pathways of 2-MIB and geosmin photocatalytic oxidation in the presence of Fe-N co-doped TiO2

In this study, 2-methylisoborneol (2-MIB) and geosmin (GSM) were degraded through photocatalytic oxidation process. For 2-MIB degradation under visible light irradiation, the highest removal rate was obtained in the presence of the 0.001% Fe – 0.5% N co-doped TiO2 calcined at 500 °C. The removal rates of 2-MIB and GSM were significantly affected by the wavelength of the lamp used during the oxidation, with the effective order of 254 nm > 365 nm > 420 nm > 475 nm. Higher steady-state concentration of ·OH, which was obtained at shorter wavelength, led to higher T&O removal efficiency. The degradation intermediates of 2-MIB and GSM during the photocatalytic oxidation, including a series of alcohols, aldehydes and ketones, were associated with the dehydration and ring-opening pathways. In most cases, for 2-MIB photocatalytic degradation, intermediates with ring structure were yielded under visible light, while the chain compounds tended to be generated under UV irradiation. However, intermediate products of GSM were not varied from each other significantly when the wavelength changed. The abundances of the GSM degradation intermediates were larger than those of the 2-MIB degradation intermediates because GSM was easier to be oxidized than 2-MIB. The apparent degradation rates of 2-MIB and GSM in real water were lower than those in deionized water, and the humic substances in real water were decomposed into low-molecular weight substances.

The Hazardous Origin of Photocatalytic Activity of ZnCr2O4

The ZnCr2O4 catalysts are synthesized by thermal decomposition of (NH4)2[Zn(NH3)2(CrO4)2] and materials with high surface areas and particle sizes in the nano regime are obtained. A special structural feature of the materials are stacking faults with densities strongly depending on the synthesis temperature, i.e. the lower the temperature the larger the number of stacking faults. The catalyst prepared at the lowest decomposition temperature exhibiting the smallest particle size shows the highest catalytic activity in the photocatalytic degradation of y‐Eosin in a photo‐Fenton process. The results of different analytic methods demonstrate that the high catalytic activity is directly correlated with CrO42– anions generated via photo‐oxidation of the catalyst. Therefore, ZnCr2O4 cannot be regarded as an environmental friendly catalyst for advanced photocatalytic oxidation processes.

Integration of Photocatalytic Oxidation and Biodegradation Treatment Processes to Enhance Degradation Efficiency of CETP Wastewater Contaminants

In the present, experiment reported an emerging approach of integrated treatment processes such as photocatalytic oxidation and biodegradation to increase degradation efficiency of CETP wastewater. Photocatalytic oxidation process performed using hybrid photocatalyst Ti02 impregnated with activated carbon (AC) and biodegradation was performed by developed biofilm on biocarrier. Synthesized TiO2/AC powder was characterized by sophisticated instrumentation. A lab scale photocatalytic bioreactor was designed to remove pollutants from CETP effluent. In this setup, sample was treated with hybrid photocatalyst TiO2/AC under the sunlight and developed biofilm; sampling was done and analyzed. Our results show better degradation within 6 h because of generation of hydroxyl radical and superoxide species reacted with pollutants. This presented experiment shows the rapid degradation and increase removal efficiency of pollutants by using the integrated processes.

Efficient photocatalytic oxidation of arsenite from contaminated water by Fe2O3-Mn2O3 nanocomposite under UVA radiation and process optimization with experimental design

The efficiency of photocatalytic oxidation process in arsenite (As(III)) removal from contaminated water by a new Fe2O3-Mn2O3 nanocomposite under UVA radiation was investigated. The effect of nanocomposite dosage, pH and initial As(III) concentration on the photocatalytic oxidation of As(III) were studied by experimental design. The synthesized nanocomposite had a uniform and spherical morphological structure and contained 49.83% of Fe2O3 and 29.36% of Mn2O3. Based on the experimental design model, in photocatalytic oxidation process, the effect of pH was higher than other parameters. At nanocomposite concentrations of more than 12 mg L−1, pH 4 to 6 and oxidation time of 30 min, photocatalytic oxidation efficiency was more than 95% for initial As(III) concentration of less than 500 μg L−1. By decreasing pH and increasing the nanocomposite concentration, the photocatalytic oxidation efficiency was increased. Furthermore, by increasing the oxidation time from 10 to 240 min, in addition to oxidation of As(III) to arsenate (As(V)), the residual As(V) was adsorbed on the Fe2O3-Mn2O3 nanocomposite and total As concentration was decreased. Therefore, Fe2O3-Mn2O3 nanocomposite as a bimetal oxide, at low doses and short time, can enhance and improve the efficiency of the photocatalytic oxidation and adsorption of As(III) from contaminated water resources. Furthermore, the energy and material costs of the UVA/Fe2O3-Mn2O3 system for photocatalytic oxidation of 1 mg L−1 As(III) in the 1 L laboratory scale reactor was 0.0051 €.

A facile method to prepare translucent anatase thin films in monolithic structures for gas stream purification.

In the present work, a facile method to prepare translucent anatase thin films on cellulose acetate monolithic (CAM) structures was developed. A simple sol-gel method was applied to synthesize photoactive TiO2 anatase nanoparticles using tetra-n-butyl titanium as precursor. The immobilization of the photocatalyst on CAM structures was performed by a simple dip-coating method. The translucent anatase thin films allow the UV light penetration through the CAM internal walls. The photocatalytic activity was tested on the degradation of n-decane (model volatile organic compound-VOC) in gas phase, using a tubular lab-scale (irradiated by simulated solar light) and pilot-scale (irradiated by natural solar light or UVA light) reactors packed with TiO2-CAM structures, both equipped with compound parabolic collectors (CPCs). The efficiency of the photocatalytic oxidation (PCO) process in the degradation of n-decane molecules was studied at different operating conditions at lab-scale, such as catalytic bed size (40-160cm), TiO2 film thickness (0.435-0.869μm), feed flow rate (75-300cm3min-1), n-decane feed concentration (44-194ppm), humidity (3 and 40%), oxygen concentration (0 and 21%), and incident UV irradiance (18.9, 29.1, and 38.4WUVm-2). The decontamination of a bioaerosol stream was also evaluated by the PCO process, using Pseudomonas aeruginosa (Gram-negative) and Staphylococcus aureus (Gram-positive) as model bacteria. A pilot-scale unit was operated day and night, using natural sunlight and artificial UV light, to show its performance in the mineralization of n-decane air streams under real outdoor conditions. Graphical abstract Normally graphics abstract are not presented with captions/legend. The diagram is a collection of images that resume the work.

Improving visible-light-driven photocatalytic NO oxidation over BiOBr nanoplates through tunable oxygen vacancies

In this work, a series of BiOBr nanoplates with oxygen vacancies (OVs) were synthesized by a solvothermal method using a water/ethylene glycol solution. The number of OVs and facets of BiOBr were tuned by changing the water/ethylene glycol ratio. Although the role of OVs in photocatalysis has been investigated, the underlying mechanisms of charge transfer and reactant activation remain unknown. To unravel the effect of OVs on the reactant activation and photocatalytic NO oxidation process, in situ diffuse reflectance infrared Fourier transform spectroscopy, so-called DRIFTS, and theoretical calculations were performed and their results combined. The photocatalytic efficiency of the as-prepared BiOBr was significantly increased by increasing the amount of OVs. The oxygen vacancies had several effects on the photocatalysts, including the introduction of intermediate energy levels that enhanced light absorption, promoted electron transfer, acted as active sites for catalytic reaction and the activation of oxygen molecules, and facilitated the conversion of the intermediate products to the final product, thus increasing the overall visible light photocatalysis efficiency. The present work provides new insights into the understanding of the role of OVs in photocatalysts and the mechanism of photocatalytic NO oxidation.

Nitric oxide removal by action of ZnO photocatalyst hydrothermally synthesized in presence of EDTA

ZnO samples with different morphologies were synthesized in presence of ethylenediaminetetraacetic acid disodium salt (EDTA) at 200 °C under hydrothermal treatment. The morphology of the nanostructures obtained was modified by changing the concentration of EDTA and the reaction time. The effect of the reaction conditions on the morphology, crystallization as well as in the optical and textural properties of the ZnO samples was investigated by using scanning electron microscopy (SEM), X-ray powder diffraction (XRD), UV–Vis absorption spectroscopy (DRS) and adsorption-desorption N2 isotherms (BET). The ZnO performance as photocatalyst was evaluated in the oxidation reaction of nitric oxide (NO) under UV irradiation. The study revealed that ZnO samples with morphology of nanoplates showed significantly higher NO removal than other ZnO samples with morphologies of rods and flower-type. The ZnO sample with the highest photocatalytic activity was measurement using different mass and its stability was tested after several photocatalytic cycles. By the use of scavenger species was determined the participation mainly of the superoxide anion (O2.-) and holes (h+) in the photocatalytic oxidation process of NO.

Template-Free Hydrothermal Synthesis, Mechanism, and Photocatalytic Properties of Core–Shell CeO2 Nanospheres

CeO2 nanospheres with the core–shell nanostructure have been successfully synthesized by a template-free hydrothermal method. The structures, morphologies and optical properties of core–shell CeO2 nanospheres were analyzed by X-ray diffraction (XRD), TG, Fourier transform infrared spectroscopy, XRD, EDS, SAED, scanning electron microscopy and transmission electron microscopy, UV–Vis diffuse reflectance spectra, Raman analyses. The degradation efficiencies of core–shell CeO2 nanospheres for methyl orange were as high as 93.49, 95.67 and 98.28% within 160 min, and the rates of photo degradation of methyl orange by core–shell CeO2 nanospheres under UV-light were 0.01693, 0.01782 and 0.02375 min−1. Methyl orange was degraded in photocatalytic oxidation processes, which mainly gave the credit to a large number of reactive species including h+, surface superoxide species ·O2−, and ·OH radicals. The core–shell structure, small crystallite size and the conversion between Ce3+ and Ce4+ of CeO2 nanospheres were of importance for its catalytic activity. These results demonstrated the possibility of improving the efficient catalysts of the earth abundant CeO2 catalysts.

Treatment and reclamation of hydrocarbon-bearing oily wastewater as a hazardous pollutant by different processes and technologies: a state-of-the-art review

AbstractHydrocarbon-containing oily wastewater generated by various industries creates a major environmental problem all over the world since petroleum products are commonly used as energy sources and raw materials in various industries. In case of offshore/coastal oil recovery operations, produced water is discharged through either shore side outfalls or coastal rim releases. In many cases, current disposal practices leads to severe environmental pollution by contamination of petroleum hydrocarbon to the surface, ground, and coastal waterways. Therefore, it is necessary to evaluate the performance of various processes for the recovery of petroleum hydrocarbons from wastewater. In this paper, a detailed review on the different separation/treatment processes of oily wastewater is presented. Previous and recent research works are reviewed in the area of oil-water separation from wastewater and also highlight the new developments in these areas. Various separation processes and technologies such as gravity separation, flotation process, membrane process, adsorption process, biological treatment, freeze/thaw process, and photocatalytic oxidation process (PoPs)/advanced oxidation processes (AoPs) are discussed and reviewed. The adsorption properties of a wide variety of porous sorbent materials in oily wastewater treatment, particularly in the area of oil spill cleanup, are also reviewed. The advantages and disadvantages of each process are critically discussed and compared.

Photocatalytic oxidation process (UV-Fe2O3) efficiency for degradation of hydroquinone

Photocatalytic oxidation process (UV-Fe2O3) efficiency for degradation of hydroquinone

Preparation, Characterization and Application of Nano ZnO - Blended Polymeric Membrane

Effluents from dyeing and finishing processes of textile industry contain strong colour and possible heavy metals. Conventional treatments are applied to treat dyes but the secondary pollution problem not addressed. Consequently, the heterogeneous photocatalytic oxidation process is of special interest. In this work a cellulose acetate-polyethylene glycol-polyurethane membrane impregnated with nano ZnO as a photocatalyst was prepared. The prepared membranes characterized by IR, SEM with EDAX and pure water flux (PWF). The photocatalytic degradation of dyes using prepared membrane was investigated towards the removal of Reactive red and Reactive orange. The kinetic model of Langmuir-Hinshelwood well describes the photodegradation capacity.

Template‐free Fabrication of ZnS/TiO2 Photocatalyst with Macrochannels

Constructing a porous structure in photocatalysts is an effective strategy for improving the photocatalytic activity because of its enhanced molecule transfer capability and light capturing efficiency. In this work, a hierarchical macro‐/mesoporous ZnS/TiO2 composite with macrochannels was successfully synthesized without using templates by the simple dropwise addition of an ethanol solution of tetrabutyl titanate and zinc acetate into a sodium sulfide aqueous solution, which was then calcined at 450°C. Compared with pure TiO2, the ordered porous ZnS/TiO2 composite exhibited an enhanced photocatalytic activity on methylene blue removal under UV‐light irradiation. The results indicate that the macro‐/mesoporous structure, the large specific surface area, and the heterostructure combination between ZnS and TiO2 play a synergistic effect on the enhanced photocatalytic activity via improving the light absorption and the diffusion of organic molecules, providing more reactive sites for the photocatalytic reaction and improving the separation of photogenerated electron–hole pairs, respectively. Radical trapping experiments demonstrated that holes (h+) and superoxide anion radicals (O2−) play an important role in the photocatalytic oxidation process.