Individual Photocatalysis Research Articles

Optimizing catalytic performance of Ag2O/Na0.5Bi0.5TiO3 heterojunction by the piezo-phototronic coupling effect

The constructing of heterojunction piezo-photocatalysts has been regarded as a promising strategy in environmental remediation. Herein, a novel Ag2O/Na0.5Bi0.5TiO3 (Ag2O/NBT) p-n heterojunction is designed by using a facile method, inducing the remarkable enhancement of photocatalytic performance by piezoelectric effect under ultrasonic vibration. The Ag2O/NBT heterojunction can degrade 99 % Rhodamine B (RhB) within 30 min when exposed to light irradiation and ultrasonic vibration simultaneously, with a high reaction rate constant of 0.140 min−1, which is 4.5 times and 17.5 times that of individual photocatalysis (0.031 min−1) and piezocatalysis (0.008 min−1), respectively. Moreover, the Ag2O/NBT heterojunction exhibits excellent stability and reusability after five cycles. The improved piezo-photocatalytic performance can be attributed to the formation of p-n heterojunction and the generation of built-in electric field, which makes a high separation of photogenerated carriers. Finally, a possible piezo-photocatalytic mechanism for removal RhB was proposed based on the radical trapping experiment. It is expected that the results can provide valuable information for the further investigations of Ag2O/NBT heterojunction as a potential piezo-photocatalyst in the environmental remediation.

Zr-UiO-66, ionic liquid (HMIM+TFSI−), and electrospun nanofibers (polyacrylonitrile): All in one as a piezo-photocatalyst for degradation of organic dye

The synergistic effect provided by combining piezocatalysis and photocatalysis can assure the future of water cleaning. The Zr-UiO-66 (ZrU) piezo-photocatalyst was first synthesized through the solvothermal process and then followed by the incorporation with the liquid-based piezocatalyst of HMIM+TFSI− at three different concentrations to provide ZrU@ILs, which were subsequently incorporated into the piezocatalytic matrix of polyacrylonitrile (PAN). The solution of ZrU@IL/PAN was then subjected to electrospinning to fabricate the ZrU@IL/PAN nanofibers (NFs). Among the three dye models, Rhodamine B (RhB) was more degraded and the order of ZrU@IL/PAN NFs > ZrU/PAN NFs > ZrU@IL > IL/PAN NFs > pure PAN NFs > ZrU > HMIM+TFSI− was observed for its degradation in exposure to both ultrasonic (US) vibration and light radiation, approving the boosted influence of the three catalytic components of ZrU, HMIM+TFSI−, and PAN NFs in the degradation of RhB and more effectiveness of the fibrous form of catalysts compared to their corresponding catalytic powders. A synergistic effect was detected in the piezo-photodegradation efficiencies of RhB (2.2 %-95.4 %) compared to the individual photodegradation (0.0 %-21.3 %) and individual piezodegradation efficiencies (2.3 %-84.2 %). The ZrU@IL-1/PAN NFs as the optimal piezo-photocatalyst displayed high recycling after four cycles of usage, RhB mineralization percentage of 67 % within 40 min, and a pseudo-first-order kinetic rate constant being 1.67 and 12.8 times higher than that of individual piezocatalysis and individual photocatalysis. Tauc plots and Mott-Schottky measurements in agreement with the radical trapping experiments suggested the main role of O2•- and HO• species in the RhB degradation mechanism. LC-MS-MS was applied to clarify the intermediates generated during the RhB piezo-photodegradation process.

Controversial mechanism of simultaneous photocatalysis and Fenton-based processes: additional effect or synergy?

Many published articles have reported the advantages of coupling photocatalysis and Fenton-based processes for environmental remediation purposes, especially wastewaters treatment, but without providing detailed discussion on how and why the resulting process is better, thus leading to misconception about their synergy. In this work, the context of the water pollution is presented along with the pros and cons of individual photocatalysis and Fenton-based processes. The simultaneous triggering of these two advanced oxidation processes is critically discussed from both performance and mechanism sides since additional effect and synergy are often misunderstood in the literature. Insights into research approaches to clarify the synergistic mechanism between photocatalysis and Fenton-based processes are also provided. One of the key features is to assess the separated contribution of the individual processes and also to elucidate the charge carriers' dynamics at the surface of the catalyst. The aim of this work is to inform scientists about the complexity of simultaneously triggered photocatalysis and Fenton-based processes but also to highlight the potential development of a new generation of catalysts that might be integrated to current wastewater treatment technology to achieve higher efficiency and their implications in the circular economy of water.

Impact of pretreatment with photocatalysis sequential coupling Fenton oxidation on physicochemical properties, pyrolysis behaviors, and product distribution of walnut shell

Naturally occurring alkali and alkaline earth metals (AAEMs) in biomass can adversely affect its pyrolysis behavior and product distribution and contribute to ash deposition in boilers. To address these challenges, we proposed a new idea of photocatalysis sequential coupling Fenton oxidation for biomass pretreatment. Our findings revealed that sequential pretreatment has the optimal moderating effects on biomass relative to individual photocatalysis and Fenton oxidation. The lignin and AAEMs in biomass were effectively reduced via sequential pretreatment, which was accompanied by cellulose content increased by 80.78% relative to untreated. Also, the slagging/fouling inclinations of biomass were successfully alleviated, and the pyrolysis performance was effectively improved. The kinetic parameters obtained based on the Coats-Redfern method can characterize the pyrolysis behavior well. During fast pyrolysis, sequential pretreatment caused the productivity of bio-oil was increased by 30.14% relative to untreated. In particular, the productivity of levoglucosan in bio-oil was increased by 364.71%. This study presented a novel and effective pretreatment strategy to improve the pyrolysis behavior and product distribution of biomass and alleviate ash deposition problems in boilers.

Efficient piezo-photocatalysis of Bi2O2(OH)NO3/BiOI heterojunction: Collaboration of piezoelectric polarization and interface electric field

Effective removal of recalcitrant pollutants is crucial for environmental protection. Tetracycline hydrochloride, as a representative recalcitrant organic pollutant, poses a potential threat to environmental integrity when present in aquatic ecosystems. Coupling piezoelectric polarization, capable of considerably promoting the photocharge separation, acts as a very prevalent and attractive strategy to improve the photocatalytic activity. In this study, an efficient piezo-photocatalytic system was developed in Bi2O2(OH)NO3/BiOI heterojunction by collaborating with interfacial electric field and vibration-induced piezoelectric polarization. The construction of type II heterojunction allows an interfacial electric field to propel the photogenerated electrons from BiOI to Bi2O2(OH)(NO3) under visible light irradiation. The introduction of vibration-induced piezoelectric polarization field strengthens the interfacial electric field, which further promote the separation and migration of photogenerated charges. Profiting from the above advantages, Bi2O2(OH)(NO3)/BiOI heterojunction exhibited a remarkable piezo-photocatalytic performance, achieving an over 80% degradation efficiency of tetracycline hydrochloride within 10 min, which far surpasses that under individual photocatalysis or ultrasound-induced piezocatalysis and also exceeds most of the previously reported piezo-photocatalysts. The combination of electron paramagnetic resonance, piezoresponse force microscopy, COMSOL simulation, and photoelectrochemical tests are conducted to probe the synergistically-catalytic mechanism. This work not only elucidates the comprehensive impact of interfacial electric field and piezoelectric polarization on charge separation, but also highlights the tremendous potential of piezo-photocatalysis for environmental remediation.

Efficient wastewater treatment in petroleum refineries: Hybrid electro-fenton and photocatalysis (UV/ZnO) process

In this study, a new hybrid system composed of a photo-catalysis (UV/ZnO) process combined with an electro-Fenton (EF) process equipped with a micro porous graphite air diffusion cathode (MPGADC) was used to treat petroleum refinery wastewater (PRW). The hybrid system was operated in a batch recycle mode and its performance was investigated and optimized using a response surface methodology (RSM). Three operating parameters affecting on the removal efficiency (RE%) of chemical oxygen demand (COD) were investigated including current density (2–10 mA/cm2), ZnO dosage (0.05–0.35 g/L), and Fe2+concentration (0.05–0.15 mM). Results showed that the optimum operating conditions can be achieved using a current density of 6.44 mA/cm2, with ZnO dosage of 0.35 g/L, and concentration of Fe2+ ions at 0.05 mM in which RE% of 90.15% was obtained with requiring a total electrical energy consumption (EECT) of 19.102KWh/m3. Furthermore, analysis of variance (ANOVA) exhibited a high value of determination coefficient (R2) close to 98.24% indicating a satisfactory fit between the obtained regression model and the experimental results. Moreover, ANOVA results revealed that current density has the most significant effect on RE% with a contribution of 52.41% followed by ZnO dosage and Fe2+ concentration both of them with a contribution of 11.64%. The comparison between the individual photo-catalysis process and hybrid process showed that RE% increases from 77.83% to 90.15% making an enhancement by 15.83% in RE% while EECT decreased from 27.171to 19.102KWh/m3 making a reduction by 29.7% in EECT. Hence, combining EF with photo-catalysis process improves the efficiency and reduced the required energy in comparison with the individual photo-catalysis process. Therefore, the combined process could be considered as an alternative, sustainable, green and cost-effective method for treatment of refinery wastewaters.

The binary piezoelectric synergistic effect of KNbO3/MoS2 heterojunction for improving photocatalytic performance

Piezoelectric polarization is a promising approach to promoting the separation and transfer of charge carriers of photocatalysts by modulating energy band structure. A binary piezoelectric integrated piezo-photocatalytic heterojunction o-KNbO3/MoS2 (o-KN/MS) is fabricated through few-layered MoS2 nanosheets growth on the ferroelectric orthorhombic KNbO3 (o-KNbO3). Under simultaneous light irradiation and ultrasonication, the optimal o-KN/MS exhibits a higher piezo-photocatalytic rhodamine B degradation rate (0.16979 min−1) than individual photocatalysis (0.00981 min−1) or individual piezocatalysis (0.09419 min−1). The piezo-photocatalytic degradation rates of RhB (0.16979 min−1), Cr (VI) (0.00877 min−1), and MB (0.01017 min−1) of o-KN/MS are 2.6, 7.9, and 4.2 times as large as that of single piezoelectric hybrid piezo-photocatalyst c-KNbO3/MoS2, respectively, where c-KNbO3 in c-KN/MS refers to non-piezoelectric paraelectric cubic KNbO3 (c-KNbO3). At the same condition, the current density for o-KN/MS reaches 54.96 μA/cm2, which is 2.9 folds as high as that of c-KN/MS. These results demonstrate that the altering piezoelectric polarization from the binary piezoelectric materials promotes continuous carrier separation within o-KNbO3 and MoS2 but also on the heterojunction interface, which provides a strategy for designing integrated piezo-photocatalyst to achieve efficient pollutant degradation and enhance electrochemical performance.

Sonochemical synthesis of Ce-TiO2 nanocatalyst and subsequent application for treatment of real textile industry effluent

Treatment of real textile industry effluent using photocatalysis, sonocatalysis, sonophotocatalysis and H2O2 assisted sonophotocatalysis have been studied based on the use of Ce-TiO2 nanocatalyst synthesized using sonochemical co-precipitation method. Characterization studies of the obtained catalyst revealed crystallite size as 1.44 nm with particles having spherical morphology. A shift of the absorption edge to the visible light range was also observed in UV–Vis diffuse reflectance spectra (UV-DRS) analysis. The effects of different operational parameters viz catalyst dose (0.5 g/L-2 g/L), temperature (30 °C-55 °C) and pH (3–12) on the COD reduction were studied. The reduction in the COD was higher at lower pH and the optimum temperature established was 45 °C. It was also elucidated that the required catalyst dose was lesser in combined sonophotocatalysis when compared with individual photocatalysis and sonocatalysis. Combination of processes and addition of oxidants increased the COD reduction with the sonophotocatalytic oxidation combined with H2O2 treatment showing the best results for COD reduction (84.75%). The highest reduction in COD for photocatalysis was only 45.09% and for sonocatalysis, it was marginally higher at 58.62%. The highest reduction in COD achieved by sonophotocatalysis was 64.41%. Toxicity tests coupled with Liquid Chromatography Mass Spectrometry (LC-MS) analysis revealed that there were no additional toxic intermediates added to the system during the treatment. Kinetic study allowed establishing that generalized kinetic model fits the experimental results well. Overall, the combined advanced oxidation processes showed better results than the individual processes with higher COD reduction and lower requirement of the catalyst.

Band shifting triggered ·OH evolution and charge separation enhanced H2O2 generation in piezo-photocatalysis of Silleń-Aurivillius-structured Bi4W0.5Ti0.5O8Cl

Photocatalytic oxygen activation shares a broad prospect as it reveals a giant potential in advanced oxidation and H2O2 production. This work demonstrated the efficient oxygen activation via ultrasonic/visible-light triggered piezo-photocatalysis of Bi4W0.5Ti0.5O8Cl, a novel Silleń-Aurivillius-structured piezoelectric material with a wide light-absorption range. The material possessed a superior oxygen activation performance in piezo-photocatalysis that far exceeded that in the individual photocatalysis or piezocatalysis. In situ electrochemical and fluorescence measurements were introduced to analyze the mechanism of the enhanced catalytic activity systematically. Due to the downward band shifting and anisotropic migration caused by ultrasonic induced piezo-potential, not only the oxygen reduction reaction (ORR) process in oxygen activation was kinetically facilitated, but also the VB potential of Bi4W0.5Ti0.5O8Cl was positive enough so that the water oxidation and ·OH generation reaction were thermodynamically favorable. With the boosted effect from multiple aspects, the maximum yield of H2O2 reached 530.4 μmol·h−1·g−1 by Bi4W0.5Ti0.5O8Cl catalyst without metal-deposition in non-sacrificial system. Our work illustrated the effect of charge modulation on oxygen activation in Silleń-Aurivillius-structured Bi4W0.5Ti0.5O8Cl, and delivered insight into the mechanism of piezo-enhanced photocatalytic H2O2 generation.

Efficient Dye Removal Using Fe3O4.MnO2.MoS2 Nanocomposite in Optimized Photocatalytic Ozonation Process

ABSTRACT In this study, Fe3O4.MnO2.MoS2 nanocatalyst has been fabricated for the first time and applied in the photocatalytic ozonation (PCO) process. The efficiency of this ternary heterostructure nanocomposite was evaluated in the removal of Acid Blue 113 (AB113) dye with 100 mg.L−1 concentration utilizing response surface methodology (RSM). The optimal condition of the process was attained at pH = 3, using 2 mg of the nanocatalyst and 300 mg.L−1 ozone dosage applied over 20 min. High efficiency of AB113 removal (99%) was observed at the optimal condition. In addition, the performance of the synthesized catalyst in the PCO process was investigated in the treatment of a real textile effluent sample. The PCO has been found to be more efficient than the individual photocatalysis and catalytic ozonation methods due to the synergistic effect between the two oxidation systems. The results proved that Fe3O4.MnO2.MoS2 can be used as a highly efficient catalyst in the PCO process.

NrGO wrapped Cu-ZrO2 as a multifunctional visible-light-sensitive catalyst for advanced oxidation of pollutants and CO2 reduction.

Construction of tailor made photocatalyst is the need to achieve high visible light assimilation and charge carrier separation. In this path, combination of catalytic active element (Cu), defect rich metal oxide (ZrO2) and photoactive (NrGO) is an effective strategy. Herein, NrGO wrapped Cu-ZrO2 was prepared by modified Hummers-thermal annealing-hydrothermal approach. The synergism between Cu, Zr and NrGO was studied using transient photocurrent, EIS and TEM images. Consequently, O3/NrGO@Cu-ZrO2-10/Vis synergistic system has achieved superior photocatalytic ozonation-catalytic ozonation than individual photocatalysis and ozonation. Further, the advanced oxidation process was optimized and the catalyst was efficiently used for the reduction of CO2 into useful products. Tolerance of O3/NrGO@Cu-ZrO2-10/Vis system against rhodamine B, hydroquinone, bisphenol A and p-cresol has been investigated. A plausible mechanism was proposed based on ESR studies, BODIPY fluoresence method, band gap and Mott-Schottky data. This research provides an idea of multifunctional catalyst for advanced oxidation of contaminants and CO2 reduction.

Enhanced heterogeneous photocatalytic perozone degradation of amoxicillin by ZnO modified TiO2 nanocomposites under visible light irradiation

This study investigated enhanced photocatalytic activities of ZnO–TiO2 nanocomposite for ozonation and perozone degradation of amoxicillin (AMX) from water. A simple ball milling method was successfully developed for fabrication of ZnO–TiO2. The experiments were conducted in semi-batch mode to study effect of various operational parameters onto AMX degradation by ozonation and perozone under visible light irradiation, including composite ratio, solution pH, photocatalyst dosage, H2O2, and initial AMX concentration. Besides, the AMX degradation kinetic also was fully investigated. Especially, AMX degradation mechanism was deeply discussed using scavenger test of hydroxyl radicals and characteristic data of photocatalyst. The results indicate that optimal composite ratio between ZnO nanoparticles (NPs) and TiO2 was 10. The 10%ZnO–TiO2 catalyst was proved effectively enhancement of AMX degradation due to its highly inhibition ability towards recombination of photogenerated electron-hole pairs and enriched surface hydroxyl groups. The AMX mineralization efficiency by O3/H2O2/10%ZnO–TiO2/Vis maximized (80.0%) which was higher than the sum of those in individual photocatalysis and perozone systems (69.5%). This was due to a synergistic effect between photocatalysis and perozone causing by ZnO–TiO2. The enhanced mechanism of AMX degradation was due to interfacial reactions between O3 or hydroxyl radicals with adsorbed AMX on the ZnO–TiO2's surface, which were caused by photoexcited electrons stored on ZnO–TiO2 and transferred by O3 to produce H2O2, *OH, h +VB, *O2−, and *O3−. The reusability experiment verified a high stability of ZnO–TiO2 through four consecutive cycles with a negligible change in AMX removal. These findings show that ZnO–TiO2 was the fully promising photocatalyst for advanced oxidation processes (AOPs) to remove the antibiotic residue from wastewater.

Solar light-induced injection of hot electrons and photocarriers for synergistically enhanced photothermocatalysis over Cu-Co/SrTiO3 catalyst towards boosting CO hydrogenation into C2–C4 hydrocarbons

Solar light-driven catalysis provides a viable approach for solar-to-chemical energy conversion, but it is difficult to maximize the conversion efficiency of solar energy through individual photocatalysis or photothermocatalysis. Herein, we construct a light-induced photo- and thermal-synergistic catalysis based on an adjacent Co and Cu nanoparticles co-loading on SrTiO3 nanoparticles. Under the irradiation of concentrated solar light, the SrTiO3 support is excited by ultraviolet light to induce photocatalytic effect to generate photocarriers; meanwhile, the localized surface plasma resonance-active Cu nanoparticles mainly absorb the visible-infrared light to produce hot electrons which are either quenched to generate heat or transported to active sites; finally, the active-phase Co nanoparticles converge the electrons and heat to drive CO hydrogenation into C2–C4 hydrocarbons. This study demonstrates that a rationally-designed catalyst can effectively convert solar energy to photocarriers/hot electrons and heat, and importantly, can couple them to regulate reaction pathways towards the production of value-added chemicals.

A two-stage degradation coupling photocatalysis to microalgae enhances the mineralization of enrofloxacin

The coupling of photocatalytic and algal processes has been used for the removal of widespread antibiotics. The removal capacities of the individual and the combined system against enrofloxacin were tested and compared in this work. Due to the low tolerance of the algae to enrofloxacin, the target compound was barely degraded during the individual algal treatment. In the individual photocatalytic process, the mineralization efficiency (defined as the ratio between the produced carbon dioxide and the initial) reached ∼57% with the remaining formed as transformation products. In contrast, a two-stage treatment incorporating photocatalytic and algal processes removed enrofloxacin completely and increased the mineralization efficiency to ∼64% or more. The addition of the citric acid as external co-substrate further elevated the mineralization efficiency with a factor of 1.25 compared to that of the individual photocatalysis. Different degradation products in both individual and integrated processes were identified and compared. The degradation pathways were found to involve the attack of the piperazine moiety and quinolone core. The results indicated the potential application of the combined photocatalytic-algal treatment in removal of veterinary antibiotics and improved our understanding of the underlying mechanisms and pathways.

Unique g-C3N4/PDI-g-C3N4 homojunction with synergistic piezo-photocatalytic effect for aquatic contaminant control and H2O2 generation under visible light

Herein, a g-C3N4/PDI-g-C3N4 homojunction has been fabricated for piezo-photocatalytic atrazine removal and exhibited better performance than individual photocatalysis or piezocatalysis. The introduction of PDI induces the π-π interaction facilitating electrons migration, and twists the g-C3N4 plane into a more polar porous structure with enhanced piezoelectricity. The homojunction facilitates the photoelectron transfer at the g-C3N4/PDI-g-C3N4 interfaces. The photoelectricity and the piezoelectricity of g-C3N4/PDI-g-C3N4 were assessed. The finite element simulation showed that the porous structure of the g-C3N4/PDI-g-C3N4 is essential to the enhanced piezoelectricity. Astonishingly, the piezo-photocatalytic atrazine degradation rate under an optimized condition (pH=2.97) reached 94% within 60 min. Moreover, the g-C3N4/PDI-g-C3N4 homojunction produced 625.54 μM H2O2 during the one-hour piezo-photocatalysis. Given the quenching experiments, reactive species detection and the electronic band of g-C3N4/PDI-g-C3N4, the piezo-photocatalytic mechanism has been proposed. In addition, the degradation pathways and the reduced intermediates toxicity intermediates of atrazine have been investigated.

Built-in piezoelectric field improved photocatalytic performance of nanoflower-like Bi2WO6 using low-power white LEDs

Photocatalysis technology has been proved to be a potential strategy for removal of organic dyes, however high-power light sources are generally necessary to initiate photocatalytic reaction. In this work, we employed an excellent photocatalyst of Bi2WO6 with visible light harvest and meanwhile an intrinsic ferroelectricity, which realized the efficient degradation of organic dye via the synergetic photopiezocatalysis. Through coupling the illumination by a low-power (9W) LED and the ultrasonic vibration (120W) by an ultrasonic cleaner, the nanoflower-like Bi2WO6 composed of ultrathin nanosheets showed a much more enhanced photopiezocatalysis performance for purification of organic dye than the individual photocatalysis and piezocatalysis. Furthermore, the high mineralization efficiency and the good durability of the Bi2WO6 catalyst were demonstrated. The possible mechanism of photopiezocatalysis was finally proposed, where the ultrasound-induced piezoelectric field in Bi2WO6 drove photo-generated electrons and holes to diffuse along opposite directions, consequently promoting the separation efficiency of charge carriers. This work indicates that the synergetic photopiezocatalysis by coupling irradiation and ultrasonic vibration is a promising strategy to purify organic pollutants in wastewater.

Degradation of tetracycline hydrochloride by coupling of photocatalysis and peroxymonosulfate oxidation processes using CuO-BiVO4 heterogeneous catalyst

In this study, we synthesized CuO modified BiVO4 composite (CuO-BiVO4) and used it to construct a novel coupling system, in which two processes of photocatalysis and peroxymonosulfate (PMS) oxidation processes were integrated together to synergistic remove tetracycline hydrochloride (TC−HCl). XRD, XPS, FESEM, EDS, PL and UV–vis DRS techniques were applied for characterization of the catalyst features. CASTEP procedure of MS software was employed to calculate the electronic structure of the catalyst. The catalytic performance of CuO-BiVO4+ Vis + PMS system was investigated under impact of different variables such as CuO loading amount, pH, PMS dosage, catalyst dosage, temperature and co-existing ions. Compared with the individual photocatalysis or peroxymonosulfate oxidation process, the catalytic performance of the coupling system was significantly improved. Under visible light irradiation, 100 mL of 80 mg/L TC−HCl solution was completely degraded using 2 mM PMS activated by a CuO-BiVO4 composite in 50 min without adjust pH, and the system synergistic index reached 3.04. The improved catalytic activity is due to the effective separation of photogenerated electrons-holes and the availability of more activation PMS sites. After five cycling experiments, the degradation rates of TC−HCl were reduced slightly to 94 %, which indicated the catalysts exhibited excellent reusability and stability for its practical applications. Active species trapping experiments and ESR tests confirmed that SO4·−,·OH, hVB+, O2·− and 1O2 worked together for the TC−HCl degradation. Furthermore, the possible reaction mechanism of the coupling system was proposed, and the degradation intermediates of TC−HCl were identified by LCMS. In conclusion, integration of CuO-BiVO4, Vis and PMS exhibited an excellent performance for TC−HCl degradation within 50 min reaction, which could be introduced as an effective and promising method for the wastewater treatment.

A coupled photo-piezo-catalytic effect in a BST-PDMS porous foam for enhanced dye wastewater degradation

Over the last decade, ferro-/piezo-electric materials have provided new directions to improve catalysis. However, current challenges that must be solved include secondary pollution by the piezoelectric particulates and a limited potential for reuse and recyclability. Here, we report an efficient approach of using a piezoceramic-polymer porous foam to package barium strontium titanate (BST) particulates and prevent secondary pollution, while being able to maintain a high photo-piezo-catalytic performance after 10 cycles of repeated catalytic reactions. The photo-piezo-catalysis achieves a 97.8% dye degradation and an enhanced performance of 275% when compared to individual photocatalysis by light irradiation or periodic low-frequency mechanical squeezing alone. It is suggested the photo-piezo-catalytic coupling effect combines the advantages of increased generated electron-hole pairs and the induced piezoelectric electric field leads to a higher degree of electron-hole separation. The BST-PDMS porous foam for photo-piezo-catalysis offers a potential approach in wastewater degradation via utilizing both solar energy and environmental mechanical sources. An efficient approach of using a BST-PDMS porous foam achieves an enhanced photo-piezo-catalytic coupling effect for efficient dye degradation, which achieves a high stability with almost no decrease in photo-piezo-catalytic degradation efficiency after 10 cycles of repeated catalytic reactions. The photo-piezo-catalysis realizes a 97.8% RhB dye degradation and an enhanced performance of 275% when compared to individual photocatalysis under light irradiation or regular low-frequency mechanical squeezing alone. The BST-PDMS porous foam for a coupled photo-piezo-catalytic effect for dye degradation offers a potential approach in wastewater degradation via utilizing solar energy and environmental mechanical sources. • We report an efficient approach of using a piezoceramic-polymer porous foam for catalytic dye degradation. • A coupled photo-piezo-catalytic effect has been utilized to realize an enhanced performance of 275%. • Our research demonstrates an effective method to solve secondary pollution and reusable limits for catalysis.

A promising cooperation of photocatalysis and electro-floatation for treatment of eutrophicated raw water

In this study, a coupling process of photocatalysis and electro-floatation was developed for removing algae and organic matters in eutrophicated raw water. A series of processes, such as individual photocatalysis, individual electro-floatation, photocatalysis and electro-floatation (combined process), were constructed to explore the effect on removing pollutants with these process and probing interaction mechanism of photocatalysis and electro-floatation. Results showed that the removal rate of soluble chemical oxygen demand (SCODMn), total chemical oxygen demand (TCODMn), and chlorophyll a (Chl-a) through individual photocatalysis process are 55%, 14%, and 30%, and the removal rate of above indicators through combined process are increased to 91%, 70%, and 86%. Furthermore, the presence of electro-floatation can improve the photocatalytic activity of photocatalyst, which attributes to that electro-floatation can supply abundant O2 which is beneficial for Bi4O5I2([Hmim]I)/Bi4O5I2(KI) photocatalyst to generate more active species (•O2−), as well as generate abundant floating microbubbles to enhance the mass transfer of pollutants and photocatalysts. This study will provide a new idea for the efficient treatment of algae and organic matter simultaneously from eutrophicated raw water and provide guarantee for in-situ eutrophication restoration of water body.

Potential use of green TiO2 and recycled membrane in a photocatalytic membrane reactor for oil refinery wastewater polishing

Membrane bioreactors (MBRs) have been successfully used in oil refinery wastewater treatments. However, a polishing treatment of the MBR permeate is required to remove the recalcitrant organic compounds. In this study, the coupling of a photocatalytic membrane reactor (PMR) and MBR was investigated for the treatment of oil refinery wastewater. Titanium dioxide (TiO2) nanoparticles, synthesised by a cleaner route assisted by microwave radiation, and recycled membrane, an end-of-life reverse osmosis membrane converted to an ultrafiltration membrane by oxidation, were prepared for use as a PMR. The recycled membrane could completely retain the catalyst particles. The PMR exhibited higher efficiency and stability in the removal of organic matter than those of the individual photocatalysis and membrane processes. Adsorption of organic compounds was observed on the catalyst surface. These compounds were degraded releasing active sites for reaction/adsorption. A chemical oxygen demand analysis revealed that up to 60% of the organic matter in the MBR permeate was decomposed in the PMR, which also contributed to membrane fouling mitigation. The membrane fouling resistance in the PMR was 7.3 times lower than that in the system operated without the catalyst. In addition, membrane degradation was not observed upon the use of the catalyst. The results indicate that the PMR with the green TiO2 and recycled membrane is a highly active, stable, and promising system for the polishing of oil refinery wastewater previously treated by the MBR.