Photoelectrocatalytic Removal Research Articles

Self-enhanced photoelectrocatalytic removal of Ni-organic complex and Ni recovery by the in-situ forming anodic Ni deposit: P-n junction-driven photocatalytic oxidation and chemical oxidation

The aim of this study was to propose a novel strategy for self-enhanced Ni-organic complex decomplexation and simultaneous Ni recovery based on photoanodic Ni deposition using photoelectrocatalytic (PEC) system. Compared to the conventional PEC process, the deposition of Ni2+ on TiO2 nanorod arrays photoanode led to a 30 % increase in decomplexation efficiency for Ni-ethylenediaminetetraacetic acid (Ni-EDTA). The Ni-EDTA removal rate reached 81.0 ± 0.9 %, and the Ni recovery rate achieved 58.2 ± 0.1 % under a bicarbonate buffer condition at pH 8.5 and a current density of 0.5 mA/cm2. The anodic high-valent Ni deposit can mediate chemical oxidation of Ni-EDTA in the PEC process, which has significant potential for deep mineralization of Ni-EDTA. The formation of Ni-deposited TiO2 film significantly improved PEC activity of photoanode, as revealed by the facilitated interfacial charge transfer, suppressed charge recombination, and improved light harvesting capacity. Moreover, the photocatalytic film that exhibited p-n heterojunction characteristics associated with the accelerated electron-hole pair separation and downward shift in energy bands of TiO2, stimulated ‧OH generation during PEC process, playing a pivotal role in Ni-EDTA decomplexation. Our results highlight the potential of using anodic Ni deposition for the efficient PEC treatment of plating wastewater containing Ni-organic complex.

Coupling UiO-66 MOF with a Nanotubular Oxide Layer Grown on Ti-W Alloy Accelerates the Degradation of Hormones in Real Water Matrices.

To enable the photoelectrocatalytic treatment of large volumes of water containing low concentrations of pollutants, this study introduces a hybrid photocatalyst, composed of nanotubular oxides grown on TixW alloy (x = 0.5 and 5.0 wt %) modified with UiO-66 MOF, for degradation of estrone (E1) and 17α-ethinyl estradiol (EE2). The oxide layer (Nt/TixW) was prepared via anodization, while UiO-66 nanoparticles were synthesized by using a solvothermal process. Different techniques for modifying nanotubular oxides were evaluated to maximize the photocatalytic activity and the sorption process. In photo(electro)catalytic experiments using low concentrations of E1 and EE2 synthetic solutions and UV-vis radiation (100 W/cm2), all modified materials exhibited approximately 40% higher degradation compared to the unmodified photocatalyst, keeping the same sequential performance of the photocatalysts (Nt/TiO2 < Nt/Ti-0.5W < Nt/Ti-5.0W) independent of the treatment. This enhancement was attributed to the MOF's increased hormone sorption, with no synergistic interaction observed between the photocatalyst and the adsorbent. In real water supply matrices, the photoelectrocatalytic removal rate of E1 using Nt/Ti-5.0W modified UiO-66 under UV-vis radiation and 1.3 V was 0.168 s-1, while for EE2, it was 0.310 min-1, approximately 1.78 and 18.21 times faster than obtained with the unmodified photocatalyst. The slower degradation rate of EE2 compared to that of E1 is attributed to the formation of denser intermediates that compete with smaller organic molecules in the real matrix. The cooperative effect between NT/TixW and UiO-66 favored the confinement of pollutants and by-products within the UiO-66 cavity, minimizing the diffusion effects and promoting the degradation of these compounds by the OH· radical generated at the oxide/solution interface. Among the tested electrodes, NT/Ti5W modified with UiO-66 demonstrated the highest efficiency and stability during the recycle tests. This highlights its promise for applications in photocatalytic processes for treating water supplies with low pollutant concentrations.

The impact of suspended particulate matters on metals removal from water using a three-combined-dimensional photo-electrocatalytic reactor (case study: Sefidrud dam)

The Sefidrud dam's water contamination poses a significant health risk to millions of people. A study aimed to investigate the impact of water impurities (mostly emerging as suspended matter particles) and redox potential on the removal of heavy metals like copper, zinc, cadmium, and arsenic through a photo-electrocatalytic process. A three-dimensional photo electrocatalytic reactor with microparticles of Ti/TiO2 was used for experiments. Central Composite Design (CCD) response surface methodology was employed for optimization. The results showed removal rates of 78 % for copper, 68 % for zinc, 57 % for cadmium, and 38 % for arsenic under optimal conditions. The removal rates increased to 94 %, 86 %, 65 %, and 52 % for copper, zinc, cadmium, and arsenic in response to increased dissolved oxygen. Redox potential was found to be a governing parameter during the photo electrocatalytic removal of zinc. Furthermore, microparticles improved the removal percentage of copper and arsenic in acidic environments. Finally, chemical fractional analysis revealed that the presence of suspended matter particles (SPMs) has a detrimental impact on the performance of PEC systems. This was attributed to the desorption of metals from exchangeable and Fe-Mn bounds of SPMs during the PEC process.

Photoelectrocatalytic removal of antibiotic ciprofloxacin using a photoanode based on Z-scheme heterojunction

The photoelectrochemical method based on FTO/Fe2O3/BiOI@BiOBr photoanode was applied for the degradation of the ciprofloxacin molecule. The developed method was carried out using a reactor containing ciprofloxacin (3.0 × 10–5 mol L–1), containing a working electrode: FTO/Fe2O3/BiOI@BiOBr, a platinized titanium counter electrode and an Ag/AgCl/KCl (3.0 mol L–1) reference electrode, working potential of 2.0 V with ultraviolet radiation (9.0 W). The electrode was characterized by electrochemical, morphological, structural and optical techniques. When applying the degradation method, after one hour, the antibiotic molecule was degraded more than 90.0 %, being mineralized close to 52.0 %, in which the degraded samples were characterized by UV–vis spectrometry, determination of total organic carbon and UHPLC-Q-ToF-MS. Like this, the oxidation process proved to be efficient yielded a kinetic constant k = 3.7 × 10–2 min−1 and a half-life of 18.7 min. The charge transfer mechanism in the photoanode semiconductor material occurred by a Z-scheme recombination process. Finally, the mass spectroscopy experiments demonstrated that the ciprofloxacin oxidation process led to the formation of fourteen by-products, in which the degradation path was proposed in three steps.

Novel Ag3PO4/ZnWO4-modified graphite felt electrode for photoelectrocatalytic removal of harmful algae: Performance and mechanism

A novel Ag3PO4/ZnWO4-modified graphite felt electrode (AZW@GF) was prepared by drop coating method and applied to photoelectrocatalytic removal of harmful algae. Results showed that approximately 99.21% of chlorophyll a and 91.57% of Microcystin-LR (MCLR) were degraded by the AZW@GF-Pt photoelectrocatalytic system under the optimal operating conditions with a rate constant of 0.02617 min−1 and 0.01416 min−1, respectively. The calculated synergistic coefficient of photoelectrocatalytic algal removal and MC-LR degradation by the AZW@GF-Pt system was both larger than 1.9. In addition, the experiments of quenching experiments and electron spin resonance (ESR) revealed that the photoelectrocatalytic reaction mainly generated •OH and •O2- for algal removal and MC-LR degradation. Furthermore, the potential pathway for photoelectrocatalytic degradation of MC-LR was proposed. Finally, the photoelectrocatalytic cycle algae removal experiments were carried out on AZW@GF electrode, which was found to maintain the algae removal efficiency at about 91% after three cycles of use, indicating that the photoelectrocatalysis of AZW@GF electrode is an effective emergency algae removal technology.

Enhanced photoelectrocatalytic performance of ZnO/Co3O4 nanoflowers modified TiO2 nanotube array under visible light

The efficient degradation of organic pollutants from the water has been attracted greater public attention and remains to be the main challenge of environmental problems. In this work, ZnO/Co3O4 nanoflowers are deposited on the surface of TiO2 nanotube arrays (ZnCo-TiO2) via the one-pot hydrothermal method by adjusting the Zn/Co ratios. The images of scanning electron microscope show that the ZnCo11-TiO2 (the addition of the Zn/Co ratios is 1:1) presents nano spherical nano-flowers morphologies. In addition, the energy bandgap of ZnCo11-TiO2 is calculated to be 2.8 eV by UV–visible diffuse reflectance spectroscope, which was smaller than that of other semples. Moreover, the lowest peak intensity of photoluminescence spectroscopy for ZnCo11-TiO2 indicates that it has high electron-hole separation efficiency. From the results of UV–visible diffuse reflectance spectroscope and EIS, we can see that ZnCo11-TiO2 has a wider spectral absorption range (200–380 nm and 450–800 nm) and a smaller electron transfer impedance (137.4 Ω). The photoelectrocatalytic removal efficiencies of ZnCo11-TiO2 is 97.5% toward the removal of methylene blue (MB), which is higher than that of other semples. The excellent photoelectrocatalytic performances of ZnCo11-TiO2 are ascribed to the high visible light absorption and rapid transportation of photogenerated electrons on ZnO/Co3O4 nanoflowers. In addition, this paper tentatively stated the detailed photoelectrocatalytic mechanism of ZnCo11-TiO2 electrode for the removal of MB.

Boosted photoelectrocatalytic removal of bisphenol A in a wide spectral range on 3D BiVO4/TiO2 nanoforest

Nanostructure construction and heterojunction engineering are effective strategies for designing highly efficient photoelectrodes. Herein, we report a BiVO4 quantum dots (BQDs)/TiO2 nanoforest photoanode with 3D configuration that exhibited improved light harvesting and charge transfer efficiency. Enhanced and directional charge separation were attributed to the synergetic effect of TiO2 facet heterojunction and BiVO4/TiO2 type-II heterojunction, which were confirmed by in-situ XPS and KPFM technology. Finally, a boosted photoelectrocatalytic (PEC) bisphenol A (BPA) removal for 97.28 % in 30 min under a wide spectral range was achieved. This work offers insight into the rational design of nanostructure and heterojunction of photoelectrode.

Photoelectrocatalytic selective removal of group-targeting thiol-containing heterocyclic pollutants

The removal of a class of toxic thiol-containing heterocyclic pollutants from complex water matrices has great environmental significance. In this study, a novel photoanode (Au/MIL100(Fe)/TiO2) with dual recognition functions was designed for selective group-targeting photoelectrocatalytic removal of thiol-containing heterocyclic pollutants from various aquatic systems. The average degradation and adsorption removal efficiency of 2-mercaptobenzimidazole, 2-mercaptobenzothiazole, and 2-mercaptobenzoxazole were still above 96.7% and 13.5% after selective treatment with Au/MIL100(Fe)/TiO2 even coexisting with 10-fold concentration of macromolecular interferents (sulfide lignin and natural organic matters) and the same concentration of micromolecular structural analogues. While they were below 71.6% and 3.9% after non-selective treatment with TiO2. Targets in the actual system were selectively removed to 0.9 µg L−1, which is 1/10 of that after non-selective treatment. FTIR, XPS and operando electrochemical infrared results proved that the highly specific recognition mechanism was mainly attributable to both the size screening of MIL100(Fe) toward targets and Au-S bond formed between -SH group of targets and Au of Au/MIL100(Fe)/TiO2. •OH are the reactive oxygen species. The degradation mechanism was further investigated via excitation-emission matrix fluorescence spectroscopy and LC-MS. This study provides new guidelines for the selective group-targeting removal of toxic pollutants with characteristic functional groups from complex water matrices.

Modification of WO3 photoanode with NiFe-LDHs nanosheets array for efficient Photoelectrocatalytic removal of tetracycline

A novel WO3@NiFe-LDHs photoanode was successfully synthesized by electrochemical depositing NiFe-LDHs nanosheets array on the surface of nanoplate WO3 photoanode, in which NiFe-LDHs nanosheets formed a hetero-junction with WO3 and offered mass transfer sites to improve the bulk and interfacial charge separation of WO3@NiFe-LDHs photoanodes. In addition, TC was captured by NiFe-LDHs nanosheets, which not only facilitated the direct charge transfer for TC degradation, but also induced TC to be photo-sensitizer to enhance the light absorbance of WO3@NiFe-LDHs photoanode. Moreover, NiFe-LDHs nanosheets acted as surface catalytic sites for accelerating the water activation to generate highly oxidizing •OH. Therefore, the optional WO3@NiFe-LDHs2.5 photoanode displayed the highest PEC removal of TC with a degradation percentage of 92.3% and total organic carbon removal of 70.4% at 0.6 V (vs Ag/AgCl) bias, and showed higher photocurrent density compared with pristine WO3 photoanode. Furthermore, WO3@NiFe-LDHs photoanode showed favorable stability in the PEC degradation process, and TC was finally mineralized into CO2, H2O and some small molecular products. This work provides a deep insight on the modification of interfacial reaction to enhance the PEC degradation performance, which offered a potential route for designing PEC system with the concept of treating pollution with pollution.

2D and 3D Nanomaterials for Photoelectrocatalytic Removal of Organic Pollutants from Water

AbstractThe presence of organics in water poses a serious risk to the environment, as well as to human health. It is important to develop effective water treatment techniques that are affordable, durable, and sustainable. The removal and degradation of organic matter in water is widely explored using 2D and 3D nanomaterials, which are advantageous in providing high surface to volume ratios and favorably photoelectro activity as compared to traditional materials. The robustness of nano semiconductors has made it highly sustainable in water treatment. This review concentrates on nanostructured materials, which are demonstrating the removal of pollutants from water using various 2D and 3D nanostructured materials as photoelectrocatalytic electrodes. The 2D and 3D nanostructured materials are divided into five types according to physical morphology: nanofilms/nanosheets, nanopore structure/nanonetwork, nanoflowers, nanotubes, and other forms. Apart from this, the preparation method, characterization technology, and photoelectrocatalytic efficiency of organic pollutants degradation are reviewed. Finally, the different factors influencing degradation of organic pollutants are discussed.

Photoelectrocatalytic conversion of urea under solar illumination using Ni decorated Ti-Fe2O3 electrodes

To reduce the energy cost and environmental impact of biological nitrogen removal in wastewater treatment plants, it would be advantageous to treat urea contained in urine at the source. In this perspective, FTO/Ti-Fe2O3 (nanorods) photoelectrodes decorated with Ni as catalyst are developed and tested for urea photoelectrocatalytic oxidation under solar illumination. Gains up to 0.50 V in oxidation onset potential vs. metallic Ni are obtained thanks to a Ni photoelectrodeposition method. In situ transmission measurements (based on NiOOH light absorption) during electrochemical cycling allowed to evaluate the state of active Ni sites and confirmed that urea oxidation mechanism is of EC type. Photoelectrolyses give faradaic efficiencies of 10–18% and 9-35% for N2 and O2 formation, respectively. A significant and unexpected NO2− production (∼65%) is detected indicating another or incomplete reaction pathway. The photoelectrocatalytic removal of nitrogen from urea solutions is demonstrated but requires catalysts with higher selectivity towards N2.

Fabrication of visible-light-active Fe-2MI film electrode for simultaneous removal of Cr(VI) and phenol

In this study, a new coordination polymer of Fe-2-methylimidazole (Fe-2MI) was successfully loaded onto F-doped tin oxide (FTO) via a one-pot solvothermal method, using Fe(NO3)3 and 2MI as raw materials. For X-ray diffraction patterns (XRD) and scanning electron microscope (SEM) analysis, it can be deduced that Fe-2MI assembles were evenly dispersed on the surface of FTO, and were partially encapsulated by tiny FeOOH particles. The as-prepared Fe-2MI film electrode was used as photoanode with titanium sheet (Ti) as the cathode. Simultaneous photoelectrocatalytic (PEC) removal of phenol and Cr(VI) can be effortlessly accomplished under noticeable light illumination. Meanwhile, the impact of initial Fe state was also investigated. Fe-2MI prepared with Fe(III) behaved better PEC performance than that with Fe(II). Furthermore, the Fe-2MI photoanodes were optimized by adjusting the initial concentration of Fe(III) and 2MI precursors. Besides, the application conditions were optimized at acidic pHs and 2.5 V bias voltage. Cr(VI) can be completely reduced with 80% removal of phenol after 5 h PEC reaction. After 5 successive cyclic runs, stable photocatalytic performance can still be observed. Therefore, Fe-2MI coordination polymer can be a promising candidate for preparing visible-light-active photoanode in the application of environmental remediation.

Perspective on Photoelectrocatalytic Removal of Refractory Organic Pollutants in Water Systems

Perspective on Photoelectrocatalytic Removal of Refractory Organic Pollutants in Water Systems

A visible-light active p-n heterojunction ZnO/Co3O4 composites supported on Ni foam as photoanode for enhanced photoelectrocatalytic removal of methylene blue

A visible-light active p-n heterojunction ZnO/Co3O4 composites supported on Ni foam as photoanode for enhanced photoelectrocatalytic removal of methylene blue

Preparation of MoO3/MoS2-E composite for enhanced photoelectrocatalytic removal of antimony from petrochemical wastewaters.

By doping of MoO3 to MoS2-E, MoO3/MoS2-E composite was produced to treat the antimony (Sb+5) from raw petrochemical industry wastewater. The effects of increasing MoO3/MoS2-E composite concentrations (0.01, 0.06, 0.50, 1.20, and 6 mg/L), times (5 min, 10 min, 20 min, 60 min, 80 min), and simulated sun light powers (2, 15, and 26 mW/m2) on the removal of Sb+5 was researched. According to X-ray diffraction (XRD), MoS2-E exhibited a pure hexagonal structure with peaks at 2Ɵ data of 15.56, 33.78, 40.59, and 61.43 cm-1 while MoO3 peaks showed similar configuration with the orthorhombic stage. X-ray photoelectron spectroscopy (XPS) was used to analyze the chemical composition. After Sb+5 removal, the additional MoO3 peaks were determined at 680, 967, and 997 cm-1. XPS spectra showed that after an oxidation period, "MoS2-E" was generated. Binding energy analysis showed that Mo5+ ions were produced from the partial transformation of MoO3. The MoO3 exhibited a vertical stacking on the MoS2-E. The filtered MoS2-E graph and relevant fast Fourier transfer pictures showed octahedral phase containing a proton. Field emission scanning electron microscopy analysis results showed that nano MoO3 exhibited a nanobelt structure. The maximum 10 mg/L Sb+5 removal was 93% at 1.20 mg/L MoO3/MoS2-E composite concentration at pH = 9 after 20 min at 15 mW/m2 simulated sunlight power via photoelectrocatalysis while the maximum Sb+5 removal via adsorption was detected as 80% for the same operational conditions in unilluminated conditions.

The application of photoelectrocatalysis in the degradation of rhodamine B in aqueous solutions: a review.

The pollution of the water environment by industrial effluents is an ongoing challenge due to the rate of industrialisation and globalisation. Photoelectrocatalysis (PEC), an electrochemical advanced oxidation process, has proven to be an effective method for removing organics from wastewater. Photoelectrocatalysis is environmentally benign, cost-effective and easy to operate. In this present review, we examine the recent progress in the removal of rhodamine B dye, a common constituent of textile effluent released into the environment, through photoelectrocatalytic degradation. We present a detailed discussion on the use of different kinds of unmodified and modified photoanodes that have been explored for the photoelectrocatalytic removal of this dye. More importantly, discussions are presented on the mechanisms and kinetics of the degradation of rhodamine B dye using these photoanodes. Hence, this review will be beneficial for researchers in developing future projects in the area of wastewater treatments through photoelectrocatalysis.

Modification of Wo3 Photoanode with Tunable Nife-Ldhs Layer for Efficient Photoelectrocatalytic Removal of Tetracycline

Modification of Wo3 Photoanode with Tunable Nife-Ldhs Layer for Efficient Photoelectrocatalytic Removal of Tetracycline

Photoelectrocatalytic degradation of Rhodamine B by spray deposited Bi2WO6 photoelectrode under solar radiation

In this work, visible region active Bi2WO6 thin films with variable thickness are successfully deposited by simple and effective spray pyrolysis technique. The structural, optical, morphological and photoelectrochemical properties of synthesized thin films were studied. Rietveld refinement of the structural data tested purity and degree of crystallinity of Bi2WO6 thin films synthesized with variable solution quantity. Optical study revealed visible light absorption of films and small variation in band gap energy. A thin film deposited with 70 ml spraying solution quantity exhibit higher photocurrent density (460 mA/cm2) and same film with large area (10 × 10 cm2) was used for photocatalytic and photoelectrocatalytic degradation of Rhodamine B (RhB) dye under solar radiation. The photoelectrocatalytic removal of RhB exhibit higher degradation efficiency (94%) as compared to photocatalytic process (23%). This study can trigger potential application of Bi2WO6 photoelectrode in solar energy conversion, wastewater treatment and energy production.

Synthesis of TiO2 Photoelectrode Nanostructures for Sensing and Removing Textile Compounds Rhodamine B

The study of the sensing and removal of Rhodamine B (RhB) textile compounds is the photoelectrocatalytic system applications development. RhB was used as a model to study the performance of TiO2 (NTiO2) photoelectrode nanostructures as environmentally friendly sensors. The synthesis of NTiO2 was carried out on the surface of the Titanium electrode by applying a potential bias of 25.0 V. The NTiO2 formed on the surface of the Titanium electrode (NTiO2/Ti) was characterized using SEM, XRD, FTIR, and Cyclic Voltammetry (CV). The formation of NTiO2 is characterized by the formation of a honeycomb-like tube on the Ti electrode surface. In addition, it is strengthened by diffractogram peaks at 2ϴ = 25 o and 48 o and IR absorption at wavenumbers of 3441.01 cm-1 (-OH groups) and 1629.85 cm-1 (Ti-O group). As for the results of sensing RhB using CV, it is known that RhB is oxidized on the surface of NTiO2/Ti with a value of Ea = 1.54 V. The oxidation process that occurs is controlled by the diffusion rate. Based on the results of photoelectrocatalytic RhB removal for 60 minutes, it was shown that using 0.10 M NaCl support electrolyte effectively increased the RhB removal rate. The decrease in RhB concentration during the photoelectrocatalytic removal process was 74.21%.

Photoelectrocatalysis of paracetamol on Pd–ZnO/ N-doped carbon nanofibers electrode

The presence of pharmaceuticals in water bodies has become a major concern in recent years. An efficient and innovative way of eliminating these pollutants is through photoelectrocatalytic (PEC) degradation owing to its environmental sustainability and its ability to remove recalcitrant pollutants. In this study, palladium loaded zinc oxide/carbon nanofibers (CZnO–Pd) were employed as a novel photoanode for PEC degradation of paracetamol. The CZnO–Pd composite was prepared through electrospinning and atomic layer deposition (ALD). The obtained materials were characterized. Photoelectrochemical studies were carried out with linear sweep voltammetry and chronoamperometry. The removal efficiency was recorded using high-performance liquid chromatography coupled to a mass spectrometer detector (HPLC-MS), while the mineralization was assessed through total organic carbon (TOC) removal. The composite electrode of CZnO–Pd nanofiber showed higher photoelectrochemical activity than ZnO carbon nanofiber, which was evident in the higher photocurrent response recorded. Upon application of the material in photoelectrocatalysis, the total removal of paracetamol was achieved within 3 h with an applied current density of 10 mAcm−2. The percentage of TOC removal was 71.20 ± 0.31% after 4 h, which indicated significant mineralization. The results obtained in the present work reveal that Pd–ZnO/C has great potential for photoelectrocatalytic removal of organic micropollutants.