Novel application of a Z-scheme photocatalyst of Ag3PO4@g-C3N4 for photocatalytic fuel cells

Advanced nanofibrous photoanode for simultaneous pharmaceutical degradation and electricity generation in a photocatalytic fuel cell

Photocatalytic fuel cell technology (PFC) has emerged as an efficient solution to address the energy crisis and environmental pollution. The development of efficient, reliable, and cost-effective photoanodes remains an urgent challenge for large-scale implementation. Herein, a novel PFC system with a nanofibrous photoanode was first fabricated for simultaneous pharmaceutical wastewater treatment and electricity generation. The TiO2/1.5 %CNTs nanofibrous photoanode achieved a Voc of 0.59 V, a Jsc of 31.73 μA/cm2, and a Pmax of 3.56 μW/cm2, which was superior to the TiO2 nanofibrous photoanode. The main intermediates of phenazopyridine degradation in the PFC process were identified using LC-MS analysis. Furthermore, phytotoxicity analysis indicated that the toxicity of wastewater was eliminated after the PFC process. The results of the economic and stability analyses confirm that the TiO2/1.5 %CNTs nanofibrous photoanode exhibits low total cost, energy consumption, and long-term stability. Therefore, the nanofibrous photoanode is introduced as a promising, cost-effective, and environmentally friendly photoanode for simultaneous wastewater treatment and energy production.

Bioelectronic and photogenerated electron synergistic catalyzed removal of chlorhexidine: Degradation and mechanism

The extensive use of the antimicrobial compound chlorhexidine (CHD) has emerged as a significant threat to both the ecological environment and human health. To address this concern, a photo-electrochemical cell-microbial fuel cell (PMFC) system was studied for CHD removal by incorporating, for the first time, the photocatalysts black phosphorus/carbon nitride (BPCN) and Cu2O into the bioanode and air cathode of an MFC, respectively. By combining electrochemical, macro-genomic, and intermediate product analyses, the underlying mechanisms of bioelectronic and photoelectronic synergies were elucidated. Specifically, the bioanode and the energy band difference between BPCN and Cu2O accelerated the bioelectronic and photoelectronic transfer, reduced the reaction barrier, and enhanced the cathodic dechlorination pathway. Consequently, the PMFC showed a 31.4-fold and 8.0-fold increase in CHD removal rate compared to the MFC and PEC, respectively. The photogenerated electrons, on the other hand, acted as key cofactors, replacing cytochrome c and facilitating electron transfer at the microbial-electrode interface, which improved the system's energy yield by 53.9 %. Additionally, illumination selectively enhanced the abundance of anode functional species, carbon metabolism, and interspecific cooperation, resulting in a 4.03-fold increase in the removal of CHD and its intermediates. These findings offer new perspectives on biochemically sustainable environmental remediation for recalcitrant pollutants.

Band structure engineering, optical, transport, and photocatalytic properties of pristine and doped Nb3O7(OH): a systematic DFT study

Nb3O2(OH) has emerged as a highly attractive photocatalyst based on its chemical stability, energetic band positions, and large active lattice sites. Compared to other various photocatalytic semiconductors, it can be synthesized easily. This study presents a systematic analysis of pristine and doped Nb3O7(OH) based on recent developments in related research. The current study summarizes the modeling approach and computationally used techniques for doped Nb3O7(OH) based photocatalysts, focusing on their structural properties, defects engineering, and band structure engineering. This study demonstrates that the Trans-Blaha modified Becke-Johnson approximation (TB-mBJ) is an effective approach for optoelectronic properties of pristine and Ta/Sb-doped Nb3O7(OH). The generalized gradient approximation is used for structure optimization of all systems studied. Spin-orbit (SO) coupling is also applied to deal with the Ta f orbital and Sb d orbital in the Ta/Sb-doped systems. Doping shifts the energetic band positions and relocates the Fermi level i.e. both the valence band maximum and the conduction band minimum are relocated, decreasing the band gap from 1.7 eV (pristine), to 1.266 eV (Ta-doped)/1.203 eV (Sb-doped). The band structures of pristine and doped systems reflect direct band behavior. Investigation of the partial density of states reveals that the O p orbital and Nb d/Ta d/Sb-d orbitals contributed to the valence and conduction bands, respectively. Optical properties like real and imaginary components of the dielectric function, reflectivity, and electron energy loss function are calculated using the OPTIC program implemented in the WIEN2k code. Moreover, doped systems shift the optical threshold to the visible region. Transport properties like effective mass and electrical conductivity are calculated, reflecting that the mobility of charge carriers increases with the doping of Ta/Sb atoms. The reduction in the band gap and red-shift in the optical properties of the Ta/Sb-doped Nb3O7(OH) to the visible region suggest their promising potential for photocatalytic activity and photoelectrochemical solar cells.

Eminent destruction of organics and pathogens concomitant with power generation in a visible light-responsive photocatalytic fuel cell with NiFe2O4/ZnO pine tree-like photoanode and CuO/Cu2O nanorod cathode

Environmental conservation and energy scarcity have become two core challenges with the ever-increasing advancement of industry, particularly chemical energy rich wastewater comprising refractory organics and pathogenic microbes. Here, a multifunctional photocatalytic fuel cell (PFC) was devised using NiFe2O4 nanoparticle-loaded on pine tree-like ZnO/Zn (NiFe2O4/ZnO/Zn) photoanode and CuO/Cu2O nanorods-loaded on Cu (CuO/Cu2O/Cu) cathode for extracting electricity upon wastewater treatment. When fed with Rhodamine B (RhB) dyestuff, the NiFe2O4/ZnO/Zn-PFC provided the maximum power density (Pmax) of 0.539 mW cm-2 upon visible light irradiation with an average RhB degradation of 85.2%, which were 2.8 and 2.7 times higher than ZnO/Zn, respectively. The remarkable enhanced NiFe2O4/ZnO/Zn-PFC performance was owing to the synergistic effect of pine tree-like structure and Z-scheme heterostructure. The pine tree-like with high surface area was not only for effective harnessing photon energies but also provided more directional routes for rapid segregation and transport of carriers and higher interface contacting areas with electrolyte. Through a series of systematic characterizations, the Z-scheme heterostructure mechanism of the system and organics degradation pathway were also speculated. Additionally, the performance of the NiFe2O4/ZnO/Zn-PFC in industry printing wastewater showed Pmax of 0.600 mW cm-2, which was considerably impressive as real wastewater was challenging to accomplish. The phytotoxicity outcome also manifested that the comprehensive toxicity of RhB was eradicated after PFC treatment. Lastly, the excellent recyclability and the pronounced bactericidal effect towards Escherichia coli and Staphylococcus aureus were other attributions which enabled the NiFe2O4/ZnO/Zn-PFC for possible practical application.

Polyaniline/g-C3N4/Bi2O3/Ti photoanode for visible light responsive photocatalytic fuel cell degradation of rhodamine B and electricity generation

In order to develop efficient photoanode to improve the performance of visible light responsive photocatalytic fuel cell (PFC), in this work, polyaniline/g-C₃N₄/Bi₂O₃/Ti photoanode was successfully prepared using silica-sol drop coating method, and assembled with Cu cathode to construct PFC to decompose rhodamine B and generate electricity simultaneously. The degradation rate, maximum photocurrent density and maximum power density of this PFC were 91.23%, 0.086 mA cm^-2 and 4.78 μW cm^-2, respectively, which were 1.4 and 1.8 times, 2.4 and 4.5 times, and 1.9 and 7.3 times those of the corresponding values of the PFCs with g-C₃N₄/Bi₂O₃/Ti and Bi₂O₃/Ti photoanodes, respectively. This is attributed to the type II heterojunction structure formed among polyaniline, g-C₃N₄ and Bi₂O₃ in the polyaniline/g-C₃N₄/Bi₂O₃/Ti photoanode. Among them, polyaniline has π-π conjugated structure, which can rapidly transfer the electronic charge between g-C₃N₄ and Bi₂O₃, thus enhancing the separation efficiency of photo-generated e^--h⁺ pairs spatially and reducing their recombination, extending the visible light response wavelength of the photocatalyst, and finally improving its photocatalytic properties. This study can provide significant reference for the research of Bi₂O₃-based visible light responsive PFC.

Efficient Bias-Free Degradation of Sulfamethazine by TiO2 Nanoneedle Arrays Photoanode and Co3O4 Photocathode System under LED-Light Irradiation

Solving high electrical-energy input for pollutants degradation is one of the core requirements for the practical application of photoelectrocatalytic (PEC) technology. Herein, we developed a self-driven dual-photoelectrode PEC system (TiO2 NNs-Co3O4) composed of a TiO2 nanoneedle arrays (TiO2 NNs) photoanode and Co3O4 photocathode for the first time. Under light-emitting-diode (LED) illumination, the bias-free TiO2 NNs-Co3O4 PEC system exhibited excellent PEC performance, with an internal bias as high as 0.19 V, achieving near complete degradation (99.62%) of sulfamethazine (SMT) with a pseudo-first-order rate constant of 0.042 min−1. The influences of solution pH, typical inorganic anions, natural organic matter, and initial SMT concentration on the PEC performance were investigated. Moreover, the main reactive oxygen species (h+, •OH, •O2−) in the dual-photoelectrode PEC system for SMT decomposition were elaborated. The practical application feasibility for efficient water purification of this unbiased PEC system was evaluated. It was proved that the TiO2 NNs photoanode provided a negative bias while the Co3O4 photocathode provided a positive bias for the photoanode, which made this system operate without external bias. This work elucidated the cooperative mechanism of photoelectrodes, providing guidance to develop a sustainable, efficient, and energy-saving PEC system for wastewater treatment.

Synergy of photocatalysis and fuel cells: A chronological review on efficient designs, potential materials and emerging applications

The rising demand of energy and lack of clean water are two major concerns of modern world. Renewable energy sources are the only way out in order to provide energy in a sustainable manner for the ever-increasing demands of the society. A renewable energy source which can also provide clean water will be of immense interest and that is where Photocatalytic Fuel Cells (PFCs) exactly fit in. PFCs hold the ability to produce electric power with simultaneous photocatalytic degradation of pollutants on exposure to light. Different strategies, including conventional Photoelectrochemical cell design, have been technically upgraded to exploit the advantage of PFCs and to widen their applicability. Parallel to the research on design, researchers have put an immense effort into developing materials/composites for electrodes and their unique properties. The efficient strategies and potential materials have opened up a new horizon of applications for PFCs. Recent research reports reveal this persistently broadening arena which includes hydrogen and hydrogen peroxide generation, carbon dioxide and heavy metal reduction and even sensor applications. The review reported here consolidates all the aspects of various design strategies, materials and applications of PFCs. The review provides an overall understanding of PFC systems, which possess the potential to be a marvellous renewable source of energy with a handful of simultaneous applications. The review is a read to the scientific community and early researchers interested in working on PFC systems.

Designing Nanoengineered Photocatalysts for Hydrogen Generation by Water Splitting and Conversion of Carbon Dioxide to Clean Fuels

Semiconductor photocatalysis has received tremendous attention in the past decade as it has shown great promise in the context of clean energy harvesting for environmental remediation. Sunlight is an inexhaustible source of energy available to us throughout the year, although it is rather dilutely dispersed. Semiconductor based photocatalysis presents one of the best ways to harness this source of energy to carry out chemical reactions of interest that require external energy input. Photocatalytic hydrogen generation by splitting of water, CO₂ mitigation, and CO₂ conversion to green fuel have therefore become the highly desirable clean and sustainable processes for a better tomorrow. Although numerous efforts have been made and continue to be expended to search and develop new classes of photocatalyst materials in recent years, several significant challenges still remain to be resolved before photocatalysis can reach its commercial potential. Therefore, major attention is required towards improving the efficiencies of the existing photocatalysts by further manipulating them and parallelly employing newer strategies for novel photocatalyst designs. This personal account aims to provide a broad overview of the field primarily invoking examples of our own research contributions in the field, which include photocatalytic hydrogen generation and CO₂ reduction to value added chemicals. This account reviews the state-of-the-art research activities and scientific possibilities which a functional material can offer if its properties are put to best use through goal-oriented design by combining with other compatible materials. We have addressed fundamental principles of photocatalysis, different kind of functional photocatalysts, critical issues associated with them and various strategies to overcome the related hurdles. It is our hope that this current personal account will provide a platform for young researchers to address the bottleneck issues in the field of photocatalysis and photocatalysts with a sense of clarity, and to find innovative solutions to resolve them by a prudent choice of materials, synthesis protocols, and approaches to boost the photocatalysis output. We emphasize that a targeted or goal-directed photocatalyst nanoengineering as perhaps the only way to realize an early success in this multiparametric domain.

Construction of nitrogen vacant g-C3N4 nanosheet supported Ag3PO4 nanoparticle Z-scheme photocatalyst for improved visible-light photocatalytic activity

The superior photocatalytic activity of semiconductor-based photocatalytic materials has attracted great attention. In this work, a series of novel Ag3PO4/g-C3N4-x (APO/CNx) composites with the Z-scheme structure were fabricated through a facile precipitation method. B naphthol, a typical phenolic compound, was selected to evaluate the photocatalytic activity of all as-prepared photocatalysts. The obtained APO/CNx composites exhibited excellent photocatalytic activity for degradation of B naphthol under visible-light irradiation. Experimental results showed that the degradation rate toward B naphthol could reach to 90.5% for 180 min, which was almost 3.66 times higher than pure g-C3N4, indicating that the presence of nitrogen vacancies and Z-scheme structure could efficiently improve the photocatalytic performance of pure g-C3N4. Furthermore, the results of trapping experiments and electron spin resonance (ESR) spectroscopy manifest that •O2- and •OH radicals were the predominant active substances for B naphthol degradation, and the possible mechanism of improved photocatalytic performance was elucidated. This work will provide an innovative perspective for constructing Z-scheme photocatalysts for the application of photocatalytic in the field of wastewater treatment.

Peroxymonosulfate activated by photocatalytic fuel cell with g-C3N4/BiOI/Ti photoanode to enhance rhodamine B degradation and electricity generation

The development of traditional photocatalytic fuel cell (PFC) is severely hindered by poor visible-light response and limited reaction space. In this study, a visible-light responsive PFC with g-C₃N₄/BiOI/Ti photoanode was proposed and applied to activate peroxymonosulfate (PMS) to degrade rhodamine B. The degradation rate, maximum power density and maximum photocurrent density of the PMS/PFC system were respectively 95.39%, 103.87 μW cm^-2 and 0.62 mA cm^-2, which was respectively 1.28, 2.18, and 1.98 times that of PFC. The excellent performance is attributed to the production of more reactive oxygen species and the extension of the reaction space range after the activation of PMS. The activation pathway of PMS and charge transfer pathway of the photoanode were discussed in detail, and it was proposed that PMS was activated by Z-scheme heterojunction g-C₃N₄/BiOI/Ti photoanode.