Rare earth metal Gd influenced defect sites in N doped TiO2: Defect mediated improved charge transfer for enhanced photocatalytic hydrogen production

In this experimental studies, we report the synthesis of TiO₂ co-doped by both cationic and anionic sites by simple sol-gel based method. All the prepared samples exhibit the anatase crystalline morphology however, showed lattice distortion caused by the displacement of Ti⁴⁺ sites by Gd³⁺. The improved visible absorption is witnessed by the Gd and N co-doping with an assured redshift in the absorption edge. The N and Gd displacement inside TiO₂ lattice accompanied by the creation of OTiN and GdOTi bonds are characterized by the X-ray photoelectron spectra. The strong resonance signal by Gd4f electrons in the electron paramagnetic resonance spectroscopy further substantiate the displacement of lattice cites of TiO₂ by Gd³⁺ ions. The longevity of the photo produced charges observed in fluorescence spectra of Gd and N co-doped TiO₂ is because of the effective transfer of charges to the defect sites. The aforementioned catalysts are tested for their capacity for the H₂ production from water splitting. The 2 wt% gadolinium and nitrogen co-doped TiO₂ has shown 10764 μmol g^?1 H₂ production which is 26 times higher than the commercial Degussa P-25 catalyst. The enhanced activity for hydrogen production can be attributed to factors such as increased absorptivity under visible light and effective charge carrier separation.     

Fabrication of nano N-doped In2Ga2ZnO7 for photocatalytic hydrogen production under visible light

N-doped In₂Ga₂ZnO₇ photocatalysts were fabricated by solid state reaction route. All the prepared photocatalysts were successfully characterised by PXRD, optical absorption spectra, SEM, TEM, XPS, BET surface area and photoresponse studies. The formation of In₂Ga₂ZnO₇ was confirmed by the PXRD pattern. Optical absorption spectra showed that the visible light absorption of all the photocatalysts were enhanced by nitrogen doping. Among all the prepared photocatalysts, 1 wt% Pt loaded N-GaInZn-500 showed enhanced photocatalytic activity towards hydrogen evolution under visible light irradiation in presence of 10 vol% methanol solution as sacrificial agent. The excellent photocatalytic activity of N-GaInZn-500 is in agreement with N-content, bandgap energy, PL intensity and Surface area.     

Visible-light-enhanced catalytic hydrolysis of ammonia borane using RuP2 quantum dots supported by graphitic carbon nitride

Hydrolytic dehydrogenation of ammonia borane (AB) driven by efficient catalysts has attracted considerable attention and is regarded as a promising strategy for hydrogen generation. Herein, RuP₂ quantum dots supported on graphitic carbon nitride (g-C₃N₄) were successfully prepared by in-situ phosphorization, yielding a highly efficient photocatalyst toward AB hydrolysis. The catalysts were characterized by field-emission scanning electron microscopy, transmission electron microscopy, x-ray diffraction, x-ray photoelectron microscopy, inductively coupled plasma atomic emission spectroscopy, UV–visible diffuse reflectance spectroscopy and photoluminescence spectroscopy. A conventional water-displacement method was employed to record the hydrogen volume as a function of reaction time. Owing to visible-light irradiation, the initial turnover frequency of the AB hydrolysis was significantly enhanced by 110% (i.e., 134 min^?1) at room temperature. Furthermore, the apparent activation energy decreased from 67.7 ± 0.9 to 47.6 ± 1.0 kJ mol^?1. The photocatalytic hydrolysis mechanism and catalyst reusability were also investigated.     

In situ growth of nickel phosphide nanoparticles on inner wall of graphitic carbon nitride tubes for efficient photocatalytic hydrogen evolution

A facile two-step approach is employed to prepare novel Ni₂P@CNT hybrid photocatalyst, which is assembled by nickel phosphide (Ni₂P) nanoparticles on the inner wall of graphitic carbon nitride tube (CNT). This unique microstructure endows Ni₂P@CNT with close interfacial interaction, promotes efficient separation of photoexcited charge carriers and provides enriched sites for photocatalytic reaction. Moreover, the hybrid system is found to exhibit more superior photocatalytic hydrogen evolution activity than pure CNT and Pt-decorated CNT (Pt@CNT). As a consequence, the work illustrates the essential role of experimental process on the final morphology and performance, which is expected to pave a new method to construct various kind of excellent photocatalyst.     

Enhanced photocatalytic H2 evolution over In2S3 via decoration with GO and Fe2P co-catalysts

In this study, GO and Fe₂P were used as co-catalysts to improve the separation efficiency of photogenerated electron-hole pairs in an In₂S₃ photocatalyst. The metallic character of Fe₂P provided a cheap substitute for traditional noble metal co-catalyst for H₂ production in aqueous media. The GO/Fe₂P/In₂S₃ composite demonstrated significantly enhanced photocatalytic activity compared to pure In₂S₃, delivering a H₂ production rate of 483.35 μmol h^?1 g^?1 and a quantum yield was 22.68% under visible light irradiation. The design of the photocatalyst was optimized using “Design Expert” software. The analysis showed that a GO loading of 1.18 wt%, a Fe loading of 5.36 wt%, and a calcination temperature of 180 °C were optimal.     

Mesoporous g-C3N4 decorated by Ni2P nanoparticles and CdS nanorods together for enhancing photocatalytic hydrogen evolution

Ni₂P nanoparticles and CdS nanorods were grew together on a mesoporous g-C₃N₄ through a facile in-situ solvothermal approach. Under visible light (λ > 400 nm), the as-prepared ternary PCN–CdS-5% Ni₂P composite displays a high H₂ evolution rate with 2905.86 μmol g^?1 h^?1, which is about 14, 18 and 279 times that of PCN–CdS, PCN–Ni₂P and PCN, respectively. The enhanced photocatalytic activity is mainly attributed to the improved separation efficiency of the photocarriers by the type II PCN–CdS heterojunction and the effective extraction of photogenerated electrons by Ni₂P. Meanwhile, Ni₂P acts as co-catalyst to provide the photocatalytic active site for hydrogen reduction. In addition, PCN–CdS-5% Ni₂P composite exerts good stability in 12-h cycles.     

Anchoring single Pt atoms on hollow Ag3VO4 spheres for improved activity towards photocatalytic H2 evolution reaction

The high cost of noble metal catalysts has been a great bottleneck for the catalyst industry. Using the noble metal at a single-atom level for catalytic applications could dramatically decrease the cost. The impacts of single Pt atoms on the photocatalytic performance of Ag₃VO₄ have been investigated and reported. In this report, single Pt atoms were anchored on the surface of Ag₃VO₄ (AVO) as a cocatalyst, and the resultant composite photocatalyst has been studied for photocatalytic H₂ production from water driven by visible light. The as-prepared AVO particles are hollow nanospheres in the monoclinic phase with a bandgap of 2.20 eV. The light absorption edge of AVO/Pt is slightly red-shifted compared to that of the pristine AVO, indicating more visible light absorption of AVO/Pt. The XPS peaks of Ag, V, and Pt exhibit a significant shift after AVO and Pt get into contact, suggesting the strong interaction between the surface Ag and V atoms, and single Pt atoms. After 3-h illumination, the photocatalytic H₂ evolution amount from AVO/Pt is improved up to 1400 μmol, which is 2.8 times that on the bare AVO. Such efficient photocatalytic H₂ evolution on AVO/Pt is still maintained after five reaction cycles. The better photocatalytic performance of AVO/Pt has been attributed to the more efficient visible light utilization and the lower interfacial charge transfer resistance, as demonstrated in the DRS and EIS spectra. The presence of the surface Pt atoms also leads to a higher amount of reactive radicals, which could efficiently promote the surface redox reactions.     

A subtle review on the challenges of photocatalytic fuel cell for sustainable power production

The revolution in the arena of functional materials for the development of well advanced engineered photocatalyst can efficiently harness photon energy from a wide spectrum of electromagnetic radiation. These next-generation smart materials would be a spectacular approach in designing devices such as photovoltaic cells, photoelectrochemical cells, and photocatalytic fuel cells. Photocatalytic oxidation of water or wastewater for concurrent production of hydrogen and electric current has turned out as a principal concept for the construction of modern photocatalytic fuel cells (PFCs). Such PFCs mimics reverse photosynthesis process where electrical energy is generated from organic pollutants. In recent years many reviews on focusing the design, fabrication, and theoretical efficiency of the PFCs have been published. Hence the present review is aimed to unveil the wall-to-wall information starting from fundamentals spanning to working principles, structural configuration, electrochemical degradation of pollutants and photoelectrochemical properties, electron transport, thermodynamic behavior and columbic efficiency of studied PFCs.     

Sulfur vacancy and CdS phase transition synergistically boosting one-dimensional CdS/Cu2S/SiO2 hollow tube for photocatalytic hydrogen evolution

Constructing an efficient photoelectron transfer route to improve carrier separation efficiency is crucial for photocatalytic hydrogen evolution. In this work, CdS/Cu₂S/SiO₂ heterostructure with one-dimensional hollow tube morphology was designed by the solvothermal method using CuO/SiO₂ hollow tube as carrier. The hexagonal phase CdS and sulfur vacancies were adjusted simultaneously by the reduction strategy of NaBH₄ aqueous solution. CdS/CuS/SiO₂ with cubic phase CdS was synthesized in the absence of NaBH₄ aqueous solution. CdS/Cu₂S/SiO₂ was characterized by SEM, TEM, XRD, XPS, SPV and so on. The results showed that hexagonal CdS and sulfur vacancies benefited the separation of photo-generated carriers. As a consequence, the CdS/Cu₂S/SiO₂-10 composite exhibited a high photocatalytic hydrogen production rate (1196.98 μmol/g/h), and its performance almost 7.18 times than that of CdS/CuS/SiO₂. Moreover, CdS/Cu₂S/SiO₂-10 showed an excellent cyclic stability. This was attributed to the strong electron interaction of CdS/Cu₂S/SiO₂ heterostructure and the sulfur vacancy acted as an electron trap, enhancing the separation of photo-induced electrons and holes.     

α-Bi2O3/β-Ni(OH)2 composites: Effective solar light photocatalysts for organic pollutants degradation

α-Bi₂O₃/β-Ni(OH)₂ composites exhibited perfect photocatalytic properties for organic pollutants degradation under sunlight irradiation. Pure α-Bi₂O₃ and β-Ni(OH)₂ were prepared by coprecipitation method and then mechanically mixed in different proportions to form α-Bi₂O₃/β-Ni(OH)₂ composites. The XRD and FTIR analyses have well emphasized the formation of monoclinic α-Bi₂O₃ and hexagonal β-Ni(OH)₂ phases with high crystallinity. The SEM micrographs of α-Bi₂O₃ and β-Ni(OH)₂ powders displayed a rod and sheet shaped grains, respectively. The band gap of the pure α-Bi₂O₃ was estimated to be 2.87 eV. Pure β-Ni(OH)₂ revealed three absorption bands in the UV–visible light region. α-Bi₂O₃/β-Ni(OH)₂ composites have a more intense absorption in the visible light region compared to pure α-Bi₂O₃ sample. Modification of α-Bi₂O₃ by β-Ni(OH)₂ induced a superior photocatalytic activity especially at β-Ni(OH)₂ content of 12 wt% in α-Bi₂O₃ (BN-12 composite). This composite showed high efficiencies of 99%, 96%, 91% and 90% for methylene blue, Congo red, methyl orange and 4-niropheniol degradation in 80, 80, 180 and 300 min under sunlight irradiation, respectively. The remarkable photocatalytic activity of the α-Bi₂O₃/β-Ni(OH)₂ composite was attributed to the new states in charge separation, charge transportation and the intensive absorption of visible light. α-Bi₂O₃/β-Ni(OH)₂ composite (BN-12) has a great potential in removing of cationic and anionic dyes beside phenolic compounds from wastewater.