Processing polymer photocatalysts for photocatalytic hydrogen evolution

Conjugated materials have emerged as competitive photocatalysts for the production of sustainable hydrogen from water over the last decade. Interest in these polymer photocatalysts stems from the relative ease to tune their electronic properties through molecular engineering, and their potentially low cost. However, most polymer photocatalysts have only been utilised in rudimentary suspension-based photocatalytic reactors, which are not scalable as these systems can suffer from significant optical losses and often require constant agitation to maintain the suspension. Here, we will explore research performed to utilise polymeric photocatalysts in more sophisticated systems, such as films or as nanoparticulate suspensions, which can enhance photocatalytic performance or act as a demonstration of how the polymer can be scaled for real-world applications. We will also discuss how the systems were prepared and consider both the benefits and drawbacks of each system before concluding with an outlook on the field of processable polymer photocatalysts.

Research status and prospect of nano silver (Ag)-modified photocatalytic materials for degradation of organic pollutants

Nano silver (Ag) was metallic Ag monomers with particle size to the nanoscale. Photocatalyst was a kind of semiconductor material with photocatalytic function. Loading precious metal Ag onto semiconductor surfaces by microwave, laser-induced, solvent-thermal and hydrothermal methods could capture photogenerated electrons, reduced the compounding rate of holes and photogenerated electrons during the photocatalytic process, thereby improving the electron transfer efficiency of photocatalysis and enhancing the absorption of visible light by silver nanoparticles through the plasma resonance effect. The highly reactive free radicals produced by photocatalysts were used in the organic degradation process to degrade organic matter into inorganic matter and was a faster, more efficient and less polluting method of pollutant degradation, which has attracted a lot of attention from researchers. This review discussed the modification of various types of photocatalysts by nano Ag through different methods. The photocatalytic degradation of dyes, antibiotics and persistent organic pollutants by different modified composites was also analyzed. This review covered the several ways and means in which nano Ag has modified diverse photocatalytic materials as well as the photocatalytic degradation of dyes, antibiotics and persistent organic pollutants. This review identified the drawbacks of the existing nano Ag-modified photocatalytic materials, including their low yield and lack of recyclability, and it also offered suggestions for potential future directions for their improvement. The purpose of this review was to further research on the technology of nano Ag-modified photocatalytic materials and to encourage the creation of new modified photocatalytic nanomaterials for the treatment of organic pollutant degradation.

V-doped Ni2P nanoparticle grafted g-C3N4 nanosheets for enhanced photocatalytic hydrogen evolution performance under visible light

Exploring low-cost and highly active photocatalysts with noble metal-free cocatalysts is of great significance for photocatalytic hydrogen evolution under simulated sunlight irradiation. In this work, a novel V-doped Ni₂P nanoparticle loaded g-C₃N₄ nanosheet is reported as a highly efficient photocatalyst for H₂ evolution under visible light irradiation. The results demonstrate that the optimized 7.8 wt% V-Ni₂P/g-C₃N₄ photocatalyst exhibits a high hydrogen evolution rate of 271.5 μmol g^-1 h^-1, which is comparable to that of the 1 wt% Pt/g-C₃N₄ photocatalyst (279 μmol g^-1 h^-1), and shows favorable hydrogen evolution stability for five successive runs within 20 h. The remarkable photocatalytic hydrogen evolution performance of V-Ni₂P/g-C₃N₄ is mainly due to the enhanced visible light absorption ability, the facilitated separation of photo-generated electron-hole pairs, the prolonged lifetime of photo-generated carriers and the fast transmission ability of electrons.

Embedding Thiophene-Amide into g-C3N4 Skeleton with Induction and Delocalization Effects for High Photocatalytic H2 Evolution

Molecular skeleton modification has become a recognized method that can effectively improve the photocatalytic performance of g-C3N4 because it not only effectively promotes charge separation, but also tunes the conjugated system of g-C3N4 to make it more conducive to photocatalytic reaction. Herein, thiophene-amide embedded g-C3N4 (TA-CN-x) was successfully prepared by simple one-step thermal polycondensation using urea as a precursor and ethyl-2-amino-4-phenylthiophene-3-carboxylate (EAPC) as an additive. After embedding with thiophene-amide, the induction and delocalization effects are formed in TA-CN-x, which significantly improves the migration efficiency of photogenerated charge carriers. Meanwhile, the conjugate structure is changed due to structural modification, resulting in significant enhancement of visible light absorption compared to the pure g-C3N4 (CN). Specifically, the optimized photocatalytic H2 evolution rate of TA-CN-2 reaches 245.4 μmol·h−1, which is 8.4 times that of CN (with Pt nanoparticles as a co-catalyst), and the apparent quantum efficiency (AQY) at 450 nm is 13.6%. This work opens up a new modification process for fully tapping the photocatalytic hydrogen absorption potential of g-C3N4-based materials.

2D/2D Interface Engineering Promotes Charge Separation of Mo2C/g-C3N4 Nanojunction Photocatalysts for Efficient Photocatalytic Hydrogen Evolution

The focus of designing and synthesizing composite catalysts with high photocatalytic efficiency is the regulation of nanostructures and optimization of heterojunctions. By increasing the contact area between the catalysts, additional reaction sites can be established and charge carriers can be transferred and reacted faster. Here, two-dimensional (2D) Mo₂C is prepared via a novel approach by carbonizing precursors intercalated by low-boiling solvents, and a composite catalyst Mo₂C/graphitic carbon nitride (g-C₃N₄) with 2D to 2D structure optimization was synthesized through the self-assembly of 2D Mo₂C and 2D g-C₃N₄. The hydrogen production rate of the photocatalyst at the optimal ratio is 675.27 μmol g^-1 h^-1, which further exceeds 2D g-C₃N₄. It is 5.1 times that of the 7 wt % B/2D Mo₂C/g-C₃N₄ photocatalyst and also 3.5 times that of 0.5 wt % Pt/g-C₃N₄. The enhanced photocatalytic activity is attributed to the fact that Mo₂C as a cocatalyst can rapidly transfer the photogenerated electrons of g-C₃N₄ to the surface of Mo₂C, and the 2D to 2D structure can provide abundant reaction sites for photogenerated electrons to prevent their recombination with holes. This study provides new ideas and techniques for the development of 2D platinum-like cocatalysts and the optimization of nanojunctions.

An Overview of the Recent Progress in Polymeric Carbon Nitride Based Photocatalysis

Recently, polymeric carbon nitride (g-C₃ N₄ ) as a proficient photo-catalyst has been effectively employed in photocatalysis for energy conversion, storage, and pollutants degradation due to its low cost, robustness, and environmentally friendly nature. The critical review summarized the recent development, fundamentals, nanostructures design, advantages, and challenges of g-C₃ N₄ (CN), as potential future photoactive material. The review also discusses the latest information on the improvement of CN-based heterojunctions including Type-II, Z-scheme, metal/CN Schottky junctions, noble metal@CN, graphene@CN, carbon nanotubes (CNTs)@CN, metal-organic frameworks (MOFs)/CN, layered double hydroxides (LDH)/CN heterojunctions and CN-based heterostructures for H₂ production from H₂ O, CO₂ conversion and pollutants degradation in detail. The optical absorption, electronic behavior, charge separation and transfer, and bandgap alignment of CN-based heterojunctions are discussed elaborately. The correlations between CN-based heterostructures and photocatalytic activities are described excessively. Besides, the prospects of CN-based heterostructures for energy production, storage, and pollutants degradation are discussed.

Prominent roles of Ni(OH)2 deposited on ZnIn2S4 microspheres in efficient charge separation and photocatalytic H2 evolution

In this work, Ni(OH)₂-deposited ZnIn₂S₄ microspheres (Ni(OH)₂/ZnIn₂S₄) were fabricated using a hydrothermal process, followed by a facile in situ precipitation method. It was demonstrated that the deposition of Ni(OH)₂ on ZnIn₂S₄ effectively promotes the separation of charges photogenerated over ZnIn₂S₄, and significantly enhances photocatalytic H₂ evolution. The optimum rate of the photocatalytic H₂ evolution over the 6% Ni(OH)₂/ZnIn₂S₄ composite reaches 4.43 mmol g⁻¹ h⁻¹, which is 21.1 times higher than that of the pure ZnIn₂S₄. Based on various characterization results and Au photo-deposition on the composite, it was proposed that the capture of the photogenerated holes by the deposited Ni(OH)₂ would be responsible for the efficient charge separation, which allows more photogenerated electrons to be left on the ZnIn₂S₄ for the reduction of H⁺ to H₂ with a higher rate.

The capture of the photogenerated holes by the deposited Ni(OH)₂ contributes to the efficient charge separation, allowing more photogenerated electrons to be left on ZnIn₂S₄ to reduce H⁺ to H₂.

Recent Advancements and Future Prospects in Ultrathin 2D Semiconductor-Based Photocatalysts for Water Splitting

Ultrathin two-dimensional (2D) semiconductor-mediated photocatalysts have shown their compelling potential and have arguably received tremendous attention in photocatalysis because of their superior thickness-dependent physical, chemical, mechanical and optical properties. Although numerous comprehensions about 2D semiconductor photocatalysts have been amassed up to now, low cost efficiency, degradation, kinetics of charge transfer along with recycling are still the big challenges to realize a wide application of 2D semiconductor-based photocatalysis. At present, most photocatalysts still need rare or expensive noble metals to improve the photocatalytic activity, which inhibits their commercial-scale application extremely. Thus, developing less costly, earth-abundant semiconductor-based photocatalysts with efficient conversion of sunlight energy remains the primary challenge. In this review, it begins with a brief description of the general mechanism of overall photocatalytic water splitting. Then a concise overview of different types of 2D semiconductor-mediated photocatalysts is given to figure out the advantages and disadvantages for mentioned semiconductor-based photocatalysis, including the structural property and stability, synthesize method, electrochemical property and optical properties for H2/O2 production half reaction along with overall water splitting. Finally, we conclude this review with a perspective, marked on some remaining challenges and new directions of 2D semiconductor-mediated photocatalysts.

Colloidal properties of the metal-free semiconductor graphitic carbon nitride

The metal-free, polymeric semiconductor graphitic carbon nitride (g-CN) family is an emerging class of materials and has striking advantages compared to other semiconductors, i.e. ease of tunability, low cost and synthesis from abundant precursors in a chemical environment. Efforts have been done to improve the properties of g-CN, such as photocatalytic efficiency, designing novel composites, processability and scalability towards discovering novel applications as a remedy for the problems that we are facing today. Despite the fact that the main efforts to improve g-CN come from a catalysis perspective, many fundamental possibilities arise from the special colloidal properties of carbon nitride particles, from synthesis to applications. This review will display how typical colloid chemistry tools can be employed to make 'better g-CNs' and how up to now overseen properties can be levered by integrating a colloid and interface perspective into materials chemistry. Establishing a knowledge on the origins of colloidal behavior of g-CN will be the core of the review.

Highly Dispersible Hexagonal Carbon-MoS2 -Carbon Nanoplates with Hollow Sandwich Structures for Supercapacitors

MoS₂ , a typical layered transition-metal dichalcogenide, is promising as an electrode material in supercapacitors. However, its low electrical conductivity could lead to limited capacitance if applied in electrochemical devices. Herein, a new nanostructure composed of hollow carbon-MoS₂ -carbon was successfully synthesized through an l-cysteine-assisted hydrothermal method by using gibbsite as a template and polydopamine as a carbon precursor. After calcination and etching of the gibbsite template, uniform hollow platelets, which were made of a sandwich-like assembly of partial graphitic carbon and two-dimensional layered MoS₂ flakes, were obtained. The platelets showed excellent dispersibility and stability in water, and good electrical conductivity due to carbon provided by the calcination of polydopamine coatings. The hollow nanoplate morphology of the material provided a high specific surface area of 543 m²  g^-1 , a total pore volume of 0.677 cm³  g^-1 , and fairly small mesopores (≈5.3 nm). The material was applied in a symmetric supercapacitor and exhibited a specific capacitance of 248 F g^-1 (0.12 F cm^-2 ) at a constant current density of 0.1 A g^-1 ; thus suggesting that hollow carbon-MoS₂ -carbon nanoplates are promising candidate materials for supercapacitors.

Hydrogen peroxide-assisted synthesis of oxygen-doped carbon nitride nanorods for enhanced photocatalytic hydrogen evolution

Polymer-derived carbon nitrides based photocatalysts are very promising for solar water splitting, CO₂ reduction and environmental remediation. However, these photocatalysts still suffer from low visible light utilization efficiency, rapid recombination of photogenerated charge carriers and slow transfer kinetics. Herein, we report a hydrogen peroxide-assisted hydrothermal strategy to synthesize one-dimensional oxygen-doped carbon nitrides (OCN) for photocatalytic hydrogen evolution. A possible self-assembly mechanism is discussed. Experimental results and theoretical calculations indicate that the as-synthesized one-dimensional OCN possess narrowed band gap energy and optimized band structure, which may allow more effective visible-light harvesting and facilitate photogenerated electron–hole pair separation and transfer. As a result, the photocatalytic hydrogen evolution rates improve from 10.4 μmol h⁻¹ to 74.0 μmol h⁻¹ under visible light (λ > 400 nm), which is among the best of the reported CN-based photocatalysts for visible-light-driven hydrogen evolution. This study provides a new avenue toward the development of highly efficient carbon nitrides based photocatalysts for photocatalytic applications.

One-dimensional oxygen-doped carbon nitride nanorods synthesized via a hydrogen peroxide-assisted process exhibit enhanced hydrogen evolution under visible light.

A sulfur vacancy rich CdS based composite photocatalyst with g-C3N4 as a matrix derived from a Cd-S cluster assembled supramolecular network for H2 production and VOC removal

By calcination, a sulfur vacancy rich CdS based composite photocatalyst with graphitic carbon nitride (g-C₃N₄) as a matrix has been synthesized successfully from a tetranuclear Cd-S cluster assembled supramolecular network. In this photocatalyst (CdS@g-C₃N₄), CdS nanoparticles with a size of about 5 to 8 nm disperse homogenously in the g-C₃N₄ matrix. During calcination, some coordinated nitrogen atoms dope in the lattice of CdS and replace sulfur atoms, which generates a large number of sulfur vacancies. Under visible light irradiation, CdS@g-C₃N₄ exhibits excellent H₂ production activity with a rate achieving as high as 19.88 mmol g^-1 h^-1 in the absence of a Pt cocatalyst. Its H₂ production ability remains stable for 30 h, which does not decay. Besides H₂ production, CdS@g-C₃N₄ also shows excellent photocatalytic activity for Volatile Organic Compound (VOC) degradation. For a photocatalyst, chemical content plays an important role in its performance. Here, the influence of sulfur vacancies on H₂ production and VOC degradation is discussed in detail. We expect that the sulfur vacancy rich CdS@g-C₃N₄ can act as an efficient material for H₂ production and indoor air purification.

Silver cyanamide nanoparticles decorated ultrathin graphitic carbon nitride nanosheets for enhanced visible-light-driven photocatalysis

Silver cyanamide nanoparticle decorated carbon nitride nanosheets are synthesized to build up a type-II semiconductor heterojunction for visible-light-driven photocatalysis.

Unique physicochemical properties of two-dimensional light absorbers facilitating photocatalysis

The emergence of two-dimensional (2D) materials with a large lateral size and extremely small thickness has significantly changed the development of many research areas by producing a variety of unusual physicochemical properties.

Ultrathin 2D Photocatalysts: Electronic-Structure Tailoring, Hybridization, and Applications

As a sustainable technology, semiconductor photocatalysis has attracted considerable interest in the past several decades owing to the potential to relieve or resolve energy and environmental-pollution issues. By virtue of their unique structural and electronic properties, emerging ultrathin 2D materials with appropriate band structure show enormous potential to achieve efficient photocatalytic performance. Here, the state-of-the-art progress on ultrathin 2D photocatalysts is reviewed and a critical appraisal of the classification, controllable synthesis, and formation mechanism of ultrathin 2D photocatalysts is presented. Then, different strategies to tailor the electronic structure of ultrathin 2D photocatalysts are summarized, including component tuning, thickness tuning, doping, and defect engineering. Hybridization with the introduction of a foreign component and maintaining the ultrathin 2D structure is presented to further boost the photocatalytic performance, such as quantum dots/2D materials, single atoms/2D materials, molecular/2D materials, and 2D-2D stacking materials. More importantly, the advancement of versatile photocatalytic applications of ultrathin 2D photocatalysts in the fields of water oxidation, hydrogen evolution, CO₂ reduction, nitrogen fixation, organic syntheses, and removal pollutants is discussed. Finally, the future opportunities and challenges regarding ultrathin 2D photocatalysts to bring about new opportunities for future research in the field of photocatalysis are also presented.

Promotion of the excited electron transfer over Ni- and Co -sulfide co-doped g-C3N4 photocatalyst (g-C3N4/NixCo1-xS2) for hydrogen Production under visible light irradiation

A Ni- and Co- sulfide co-doped g-C₃N₄ photocatalyst (g-C₃N₄/Ni_xCo_1-xS₂) was prepared by hydrothermal method and this photocatalyst, namely, g-C₃N₄/Ni_xCo_1-xS₂ shown excellent photocatalytic properties due to the special structure of Ni-Co-S with boundary different exposure to active site of transition metal-metal (Ni-Co) active planes. With the introduction of Co atoms, the H₂ production amount reached the maximum about 400.81 μmol under continuous visible light irradiation for 4 hours based on the efficiently charge separation and greatly improved electron transfer resulted from the presence of sufficient active exposure at the boundary. The serial studies shown that the existence of Ni-Co-S structure over g-C₃N₄ active surface is the key factor of activity affections by means of several characterizations such as SEM, XRD, XPS diffuse reflectance etc. and the results of which were in good agreement with each other. A possible reaction mechanism over eosin Y-sensitized g-C₃N₄/Ni_xCo_1-xS₂ photocatalyst under visible light irradiation was proposed.

MoS2-Based Nanocomposites for Electrochemical Energy Storage

Typical layered transition-metal chalcogenide materials, in particular layered molybdenum disulfide (MoS2) nanocomposites, have attracted increasing attention in recent years due to their excellent chemical and physical properties in various research fieldsHere, a general overview of synthetic MoS2 based nanocomposites via different preparation approaches and their applications in energy storage devices (Li-ion battery, Na-ion battery, and supercapacitor) is presented. The relationship between morphologies and the electrochemical performances of MoS2-based nanocomposites in the three typical and promising rechargeable systems is also discussed. Finally, perspectives on major challenges and opportunities faced by MoS2-based materials to address the practical problems of MoS2-based materials are presented.

Evaluation of a multi-dimensional hybrid photocatalyst for enrichment of H2 evolution and elimination of dye/non-dye pollutants

Fabrication of 1-D ZnTiO₃ nanofibers and 2-D g-C₃N₄ based hybrid heterojunctions and their H₂ evolution from water splitting under visible light irradiation.

Graphitic carbon nitride nanosheets obtained by liquid stripping as efficient photocatalysts under visible light

Well-scattered g-C₃N₄ nanosheets obtained using a liquid stripping possess much higher photocatalytic performance than bulk g-C₃N₄.

Polyaniline/Carbon Nitride Nanosheets Composite Hydrogel: A Separation-Free and High-Efficient Photocatalyst with 3D Hierarchical Structure

A polyaniline (PANI)/carbon nitride nanosheets (CNNS) composite hydrogel with 3D hierarchical nanostructure is synthesized via in situ polymerization. The 3D hierarchical structure is robust and stable, making the composite hydrogel separation-free and easy to recycling. It is highly excellent in removing organic pollutant for PANI/CNNS composite hydrogel on account of the cooperation of adsorptive preconcentration and the following photocatalytic oxidation. Pollutants are first adsorbed and concentrated into the 3D hierarchical nanostructure of the composite hydrogel. Then the pollutants are in situ oxidized via photocatalysis. The promoted photocatalytic performance can be mainly ascribed to the outstanding interfacial charge separation and photoelectrochemical performance. A new idea of the construction of 3D hierarchical photocatalysts is presented, which can be applied in the sustainability field.

Shape-dependent photocatalytic hydrogen evolution activity over a Pt nanoparticle coupled g-C3N4 photocatalyst

A Pt decorated g-C₃N₄ photocatalyst exhibits remarkable shape-dependent photocatalytic hydrogen evolution activity.

Hybrid mesoporous Cu2ZnSnS4 (CZTS)–TiO2 photocatalyst for efficient photocatalytic conversion of CO2 into CH4 under solar irradiation

A novel design strategy is developed which demonstrates the synthesis of mesoporous p-type Cu₂ZnSnS₄(CZTS)/n-type TiO₂ heterojunction photocatalyst, with enhanced performance for its application in CO₂ photoreduction to hydrocarbon fuel, CH₄.

Facile synthesis of NiS/CdS nanocomposites for photocatalytic degradation of quinoline under visible-light irradiation

NiS/CdS nanocomposites with good visible-light-induced photocatalytic activity were successfully prepared via a facile two-step process.