Catalytic conversion of seawater to fuels: Eliminating N vacancies in g-C3N4 to promote photocatalytic hydrogen production

ZIF-8 metal-organic frameworks and their hybrid materials: emerging photocatalysts for energy and environmental applications

In the face of escalating environmental challenges such as fossil fuel dependence and water pollution, innovative solutions are essential for sustainable development. In this regard, zeolitic imidazolate frameworks (ZIFs), specifically ZIF-8, act as promising photocatalysts for environmental remediation and renewable energy applications. ZIF-8, a subclass of metal-organic frameworks (MOFs), is renowned for its large specific surface area, high porosity, rapid electron transfer ability, abundant functionalities, ease of designing, controllable properties, and remarkable chemical and thermal stability. However, its application as a standalone photocatalyst is limited by issues such as particle aggregation, poor water stability, and insufficient visible light absorption. By integrating ZIF-8 with various photoactive materials to form composite catalysts, these drawbacks can be mitigated, leading to enhanced photocatalytic efficiency. The review discusses the synthesis, properties, and applications of ZIF-8-based photocatalysts in light-driven H2 evolution, H2O2 evolution, CO2 reduction, and dye and drug degradation. It also highlights the challenges and future research directions in developing cost-effective, scalable, and environmentally friendly ZIF-8 composites for industrial applications. The potential of ZIF-8 composites to contribute to sustainable global energy solutions and environmental cleanup is significant, yet further exploration is required to harness their capabilities thoroughly.

Aerogel for Highly Efficient Photocatalytic Degradation

Photocatalysis is one of the effective ways to degrade pollutant antibiotics. Agar is used as the adsorption module to provide abundant pore structure. Carbon dots (CDs) are selected as light energy conversion components. Graphitic carbon nitride (g-C3N4) is used as the main material of the catalyst. Agar/CDs/g-C3N4-functionalized aerogel with a unique 3D pore structure is assembled. The Agar/CDs/g-C3N4 aerogel shows the highest photocurrent density, which is 3.7 times that of agar, 2.4 times that of 3-g-C3N4 and 1.6 times that of Agar/g-C3N4 aerogel. Compared with 3-g-C3N4 and Agar/g-C3N4 aerogel, which can completely remove AMX after 75 min, Agar/CDs/g-C3N4 aerogel can degrade amoxicillin (AMX) completely after 45 min of illumination. The reason is that Agar/CDs/g-C3N4 aerogel has a larger specific surface area, richer functional groups, a wider spectral range, higher photocurrent density and better carrier migration and separation efficiency. It is a good strategy with which to combine the effects of each component in the ternary system for the efficient photocatalysis of organic pollutants.

Decade Milestone Advancement of Defect-Engineered g-C3N4 for Solar Catalytic Applications

Over the past decade, graphitic carbon nitride (g-C3N4) has emerged as a universal photocatalyst toward various sustainable carbo-neutral technologies. Despite solar applications discrepancy, g-C3N4 is still confronted with a general fatal issue of insufficient supply of thermodynamically active photocarriers due to its inferior solar harvesting ability and sluggish charge transfer dynamics. Fortunately, this could be significantly alleviated by the "all-in-one" defect engineering strategy, which enables a simultaneous amelioration of both textural uniqueness and intrinsic electronic band structures. To this end, we have summarized an unprecedently comprehensive discussion on defect controls including the vacancy/non-metallic dopant creation with optimized electronic band structure and electronic density, metallic doping with ultra-active coordinated environment (M-Nx, M-C2N2, M-O bonding), functional group grafting with optimized band structure, and promoted crystallinity with extended conjugation π system with weakened interlayered van der Waals interaction. Among them, the defect states induced by various defect types such as N vacancy, P/S/halogen dopants, and cyano group in boosting solar harvesting and accelerating photocarrier transfer have also been emphasized. More importantly, the shallow defect traps identified by femtosecond transient absorption spectra (fs-TAS) have also been highlighted. It is believed that this review would pave the way for future readers with a unique insight into a more precise defective g-C3N4 "customization", motivating more profound thinking and flourishing research outputs on g-C3N4-based photocatalysis.

Confined Heterojunction in Hollow-Structured TiO2 and Its Directed Effect in Photodriven Seawater Splitting

The high salinity of seawater often strongly affects the activity and stability of photocatalysts utilized for photodriven seawater splitting. The current investigation is focused on the photocatalyst H-TiO2/Cu2O, comprised of hydroxyl-enriched hollow mesoporous TiO2 microspheres containing incorporated Cu2O nanoparticles. The design of H-TiO2/Cu2O is based on the hypothesis that the respective hollow and mesoporous structure and hydrophilic surfaces of TiO2 microspheres would stabilize Cu2O nanoparticles in seawater and provide efficient and selective proton adsorption. H-TiO2/Cu2O shows hydrogen production performances of 45.7 mmol/(g·h) in simulated seawater and 17.9 mmol/(g·h) in natural seawater, respectively. An apparent quantum yield (AQY) in hydrogen production of 18.8% in water (and 14.9% in natural seawater) was obtained at 365 nm. Moreover, H-TiO2/Cu2O displays high stability and can maintain more than 90% hydrogen evolution activity in natural seawater for 30 h. A direct mass- and energy- transfer mechanism is proposed to clarify the superior performance of H-TiO2/Cu2O in seawater splitting.

ZIF-8 metal organic framework composites as hydrogen evolution reaction photocatalyst: A review of the current state

In the past decade, extensive research has been devoted to synthesis of ZIF-8 materials for catalytic applications. As physico-chemical properties are synthesis-dependent, this review explores different synthesis strategies based the solvent and solvent-free synthesis of zeolitic imidazole framework. Accordingly, the effect of several parameters on the ZIF-8 synthesis were discussed including solvent, deprotonating agents, precursors ratio is delivered. Additionally, the advantages and disadvantages of each synthesis have been discussed and assessed. ZIF-8 textural and structural properties justify its wide use as a stable high surface area MOF in aqueous catalytic reactions. This review includes the applicatios of ZIF-8 materials in photocatalytic hydrogen evolution reaction (HER). The efficiency of the reviewed materials was fairly assessed. Finally, Limitations, drawbacks and future challenges were fully debated to ensure the industrial viability of the ZIFs.

Ni2P Nanoparticle-Inserted Porous Layered NiO Hetero-Structured Nanosheets as a Durable Catalyst for the Electro-Oxidation of Urea

The electro-oxidation of urea (EOU) is a remarkable but challenging sustainable technology, which largely needs a reduced electro-chemical potential, that demonstrates the ability to remove a notable harmful material from wastewater and/or transform the excretory product of humans into treasure. In this work, an Ni₂P-nanoparticle-integrated porous nickel oxide (NiO) hetero-structured nanosheet (Ni₂P@NiO/NiF) catalyst was synthesized through in situ acid etching and a gas-phase phosphating process. The as-synthesized Ni₂P@NiO/NiF catalyst sample was then used to enhance the electro-oxidation reaction of urea with a higher urea oxidation response (50 mA cm^-2 at 1.31 V vs. RHE) and low onset oxidation potential (1.31 V). The enhanced activity of the Ni₂P@NiO/NiF catalyst was mainly attributed to effective electron transport after Ni₂P nanoparticle insertion through a substantial improvement in active sites due to a larger electrochemical surface area, and a faster diffusion of ions occurred via the interactive sites at the interface of Ni₂P and NiO; thus, the structural reliability was retained, which was further evidenced by the low charge transfer resistance. Further, the Ni₂P nanoparticle insertion process into the NiO hetero-structured nanosheets effectively enabled a synergetic effect when compared to the counter of the Ni₂P/NiF and NiO/NiF catalysts. Finally, we demonstrate that the as-synthesized Ni₂P@NiO/NiF catalyst could be a promising electrode for the EOU in urea-rich wastewater and human urine samples for environmental safety management. Overall, the Ni₂P@NiO/NiF catalyst electrode combines the advantages of the Ni₂P catalyst, NiO nanosheet network, and NiF current collector for enhanced EOU performance, which is highly valuable in catalyst development for environmental safety applications.

2D/1D BiOI/g-C3N4 nanotubes heterostructure for photoelectrochemical overall water splitting

To boost the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performances, the BiOI/graphitic carbon nitride nanotubes (g-C₃N₄ nanotubes) heterojunction was synthesized herein through the hydrothermal method. BiOI in-situ grew on the surface of g-C₃N₄ nanotubes derived from melamine. The rapid recombination between photoexcited electrons and holes of pristine semiconductors was prevented via building the stable heterojunction. The SEM results indicated that the BiOI was wrapped around the surface of g-C₃N₄ nanotubes, resulting in an optimized electronic transmission pathway. Much lower charge transfer resistance at the p-n heterojunction was demonstrated compared with pristine BiOI according to the EIS results, thus leading to the faster surface reaction rates. Moreover, the composite exhibited both outstanding OER and HER activities under illuminated conditions. This study may shed light upon establishing a bifunctional photoelectrocatalysis for photoelectrochemical water splitting based on stable 2D metal and 1D metal-free nanocomposite.

Effects of Cu doping on electrochemical NOx removal by La0.8Sr0.2MnO3 perovskites

Electrochemical removal of nitrogen oxides (NO_x) by perovskite electrodes is a promising method due to its low cost, simple operation and no secondary pollution. In this study, a series of La_0.8Sr_0.2Mn_1-xCu_xO₃ (x = 0, 0.05, 0.1 and 0.15) perovskites are fabricated as the improved electrodes of solid electrolyte cells (SECs) for NO_x removal and the effects of Cu doping are investigated systematacially. Multiple characterization methods are carried out to analyze the physicochemical properties of perovskites firstly. Then the performances of cells based on various perovskites are evaluated by the measurements of electrochemical properties and NO_x conversions. The results show that the Cu-doped electrode has more surface oxygen vacancies and a better redox property, thus having a higher NO_x conversion and smaller polarization resistance. The electrode based on La_0.8Sr_0.2Mn_0.9Cu_0.1O₃ has the maximum 70.8% NO_x conversion and the lowest 36.3 Ω cm² R_p value in the atmosphere of 1000 ppm NO at 700 °C. First-principle calculation reveals that the Cu-doped electrode is easier to form surface oxygen vacancy, while the surface oxygen vacancy plays an important role on electron transfer between electrode and NO_x molecule. This study not only provides a new strategy to enhance the electrode performance for NO_x removal in SECs but reveals the fundamental effect of Cu doping on the properties of La_0.8Sr_0.2MnO₃ perovskites.

Facile fabrication of bifunctional SnO-NiO heteromixture for efficient electrocatalytic urea and water oxidation in urea-rich waste water

Heterostructured transition metal oxide hybrid have more attention in energy saving and environmental related field due to their higher electro-catalytic activity. In this work, we demonstrated SnO decorated with NiO nanocrystal electrocatalyst is successfully synthesized through solvothermal method and well characterized by scanning electron microscope, transmission electron microscope, X-ray diffraction and X-ray photoelectron spectroscopy. Physical characterizations confirm that spherical shape of SnO nanoparticles are homogeneously dispersed on the surface of NiO. The kinetic study of catalytic performance towards urea oxidation reaction were measured by liner sweep voltammetry and chronoamprometry. As proposed catalyst to facilitate the rate of urea oxidation reaction can increase by SnO doped NiO catalyst. The urea oxidation on SnO-NiO nanostructured modified electrode exhibits lower onset potential of 1.12 V and enhancement of current with tafel slope of 150 mV dec^-1. The obtained results demonstrated the synthesized SnO-NiO anode material could be promising electrode for urea-rich containing wastewater remediation and hydrogen production from wastewater.

NH2-MIL-125(Ti) doped CdS/Graphene composite as electro and photo catalyst in basic medium under light irradiation

The development of active electrocatalysts and photocatalysts for hydrogen evolution reaction (HER) and for environmental remediation is a huge challenge. Research is still underway on the development of low-cost catalytic materials with appreciable efficiency for HER. In the present study, a composite of metal organic framework (MOF) with CdS and graphene (NH₂-MIL-125(Ti)/CdS-graphene) composites were developed with different loadings of graphene material via solvothermal technique. Further the electrocatalytic activity of the synthesized catalysts were investigated for HER and photocatalytic degradation of dye. Results show that the synthesized catalyst with a less amount of graphene was more active. HER results showed a less Tafel slope of 70.8 and 61.9 mVdec^-1 with 15.6 mA/cm² and 15.46 mA/cm² current densities under light on and off conditions. Further the dye degradation activity of the synthesized catalysts was tested with Rhodamine B dye and results showed that the catalyst showed excellent activity for low weight loading of graphene with a degradation efficiency of 95 % and followed pseudo first order kinetic model. Overall results showed that the synthesized composites are promising for HER and photocatalytic applications.