Boron carbides as efficient, metal-free, visible-light-responsive photocatalysts

Novel C4P2 monolayers: forming Z-scheme heterojunction and Janus structure for high-efficiency metal-free photocatalytic water splitting

Metal-free two-dimensional (2D) semiconductors have garnered significant attention in the realm of photocatalytic water splitting, primarily owing to their inherent clean, stable, and efficient photoresponsive properties. Motivated by it, we have proposed two types of stable C4P2 monolayers with indirect band gaps, mediocre carrier mobility and excellent optical absorption in visible-light and ultraviolet regions. Although the too-low work function of monolayer α-C4P2 and the too-high work function of monolayer β-C4P2 make them only suitable for single-side redox reaction in photocatalytic water splitting, the creation of an α-C4P2/β-C4P2 Z-scheme heterojunction, combined with the Janus monolayer γ-C4P2 that integrates features of both α and β structures, effectively addresses this limitation, fulfilling the prerequisites for comprehensive photocatalytic water splitting. Furthermore, the calculations indicate that the α-C4P2/β-C4P2 Z-scheme heterojunction and Janus monolayer γ-C4P2 not only demonstrate improved carrier mobility and optical absorption but also feature internal electric fields that effectively enhance driving energy and photo-induced charge separation. Notably, Janus monolayer γ-C4P2 achieves a high electron mobility of ∼105 cm2 V-1 s-1 and an impressive solar-to-hydrogen conversion efficiency of 25.62%.

Photoelectrocatalytic Dioxygen Reduction Based on a Novel Thiophene-Functionalized Tricarbonylchloro(1,10-phenanthroline)rhenium(I)

A novel Re (I) complex of [Re(CO)3Cl(L)], {L = 2-([2,2’-bithiophen]-5-yl)-1-phenyl-1H-imidazo [4,5-f][1,10]phenanthroline}, was synthesized, and its optical (UV–Visible absorption and emission spectroscopy), cyclovoltammetric and photoelectrochemical oxygen reduction properties were studied. The geometric and electronic properties were also investigated by density functional theory calculations. It was found that the ITO electrode coated with drop-casted [Re(CO)3Cl(L)] film exhibited cathodic photocurrent generation characteristics. The illuminated film exhibited a maximum cathodic photocurrent up to 30.4 μA/cm2 with an illumination intensity of 100 mW/cm2 white light at a bias potential of −0.4 V vs. SCE in O2-saturated electrolyte solution, which was reduced by 5.1-fold when thoroughly deoxygenated electrolyte solution was used, signaling that the electrode performed well on the photoelectrochemical oxygen reduction. The photo-electrocatalytic hydrogen peroxide production was proved with a maximum H2O2 concentration of 6.39 μM during 5 h of the photoelectrocatalytic process. This work would guide the construction of more efficient rhenium-based photo(electro)catalytic molecular systems for O2 sensing, hydrogen peroxide production and other types of photoelectrochemical energy conversion and storage.

Exploring the photocatalytic properties and carrier dynamics of 2D Janus XMMX' (X = S, Se; M = Ga, In; and X' = Te) materials

Recently, two-dimensional (2D) Janus structures have been extensively explored because of their robust electron mobility and unique photocatalytic properties. In spite of the increasing interest, the origin of high photocatalytic activities and the behaviors of photoinduced carriers in this kind of materials have not been well understood. Herein, we present a step-by-step protocol based on the first-principles calculations combined with the ab initio non-adiabatic molecular dynamics (NAMD) simulations to unveil the origin of high photocatalytic activity of highly stable typical 2D Janus XMMX' structures (X = S, Se; M = Ga, In; and X' = Te). Their band structures, optical properties, exciton binding energies, carrier effective masses, solar-to-hydrogen efficiency, hot carrier relaxation and recombination times, etc. have been calculated. We find that the difference between X and X' atoms on the two surfaces of the XMMX' monolayer not only builds an out-of-plane electric field, which significantly affects the charge distributions on the valence band maxima (VBM) and the conduction band minima (CBM) and subsequently decreases the exciton binding energy, but also transforms the indirect band structures of XM into the direct ones with well suitable energy gaps for visible-light absorption as well as endows the XMMX' structures with unequal electron and hole mobility, rapid hot carrier relaxation and slow electron-hole recombination processes on a timescale of tens of nanoseconds. The current work suggests that Janus XMMX' monolayers are good photocatalytic materials for overall water splitting and provides a guide to regulate the materials' properties for efficient energy harvesting and optoelectronic applications.

Developing sustainable, high-performance perovskites in photocatalysis: design strategies and applications

Solar energy is attractive because it is free, renewable, abundant and sustainable. Photocatalysis is one of the feasible routes to utilize solar energy for the degradation of pollutants and the production of fuel. Perovskites and their derivatives have received substantial attention in both photocatalytic wastewater treatment and energy production because of their highly tailorable structural and physicochemical properties. This review illustrates the basic principles of photocatalytic reactions and the application of these principles to the design of robust and sustainable perovskite photocatalysts. It details the structures of the perovskites and the physics and chemistry behind photocatalytic reactions and describes the advantages and limitations of popular strategies for the design of photoactive perovskites. This is followed by examples of how these strategies are applied to enhance the photocatalytic efficiency of oxide, halide and oxyhalide perovskites, with a focus on materials with potential for practical application, that is, not containing scarce or toxic elements. It is expected that this overview of the development of photocatalysts and deeper understanding of photocatalytic principles will accelerate the exploitation of efficient perovskite photocatalysts and bring about effective solutions to the energy and environmental crisis.

Boron Carbon Oxynitride as a Novel Metal-Free Photocatalyst

Boron-based nanomaterials are emerging as non-toxic, earth-abundant (photo)electrocatalyst materials in solar energy conversion for the production of solar hydrogen fuel and environmental remediation. Boron carbon oxynitride (BCNO) is a quaternary semiconductor with electronic, optical, and physicochemical properties that can be tuned by varying the composition of boron, nitrogen, carbon, and oxygen. However, the relationship between BCNO's structure and -photocatalytic activity relationship has yet to be explored. We performed an in-depth spectroscopic analysis to elucidate the effect of using two different nitrogen precursors and the effect of annealing temperatures in the preparation of BCNO. BCNO nanodisks (D = 6.7 ± 1.1 nm) with turbostratic boron nitride diffraction patterns were prepared using guanidine hydrochloride as the nitrogen source precursor upon thermal annealing at 800°C. The X-ray photoelectron spectroscopy (XPS) surface elemental analysis of the BCNO nanodisks revealed the B, C, N, and O compositions to be 40.6%, 7.95%, 37.7%, and 13.8%, respectively. According to the solid-state 11B NMR analyses, the guanidine hydrochloride-derived BCNO nanodisks showed the formation of various tricoordinate BNx(OH)3-x species, which also served as one of the photocatalytic active sites. The XRD and in-depth spectroscopic analyses corroborated the preparation of BCNO-doped hexagonal boron nitride nanodisks. In contrast, the BCNO annealed at 600 °C using melamine as the nitrogen precursor consisted of layered nanosheets composed of B, C, N, and O atoms covalently bonded in a honeycomb lattice as evidence by the XRD, XPS, and solid-state NMR analysis (11B and 13C) analyses. The XPS surface elemental composition of the melamine-derived BCNO layered structures consisted of a high carbon composition (75.1%) with a relatively low boron (5.24%) and nitrogen (7.27%) composition, which indicated the formation of BCNO-doped graphene oxides layered sheet structures. This series of melamine-derived BCNO-doped graphene oxide layered structures were found to exhibit the highest photocatalytic activity, exceeding the photocatalytic activity of graphitic carbon nitride. In this layered structure, the formation of the tetracoordinate BNx(OH)3-x(CO) species and the rich graphitic domains were proposed to play an important role in the photocatalytic activity of the BCNO-doped graphene oxides layered structures. The optical band gap energies were measured to be 5.7 eV and 4.2 eV for BCNO-doped hexagonal boron nitride nanodisks and BCNO-doped graphene oxides layered structures, respectively. Finally, BCNO exhibited an ultralong photoluminescence with an average decay lifetime of 1.58, 2.10, 5.18, and 8.14 µs for BGH01, BGH03, BMH01, BMH03, respectively. This study provides a novel metal-free photocatalytic system and provides the first structural analysis regarding the origin of BCNO-based photocatalyst.

UV-light promoted formation of boron nitride-fullerene composite and its photodegradation performance for antibiotics under visible light irradiation

A series of C₆₀/BN composites have been synthesized, which can efficiently photodegrade TC under visible-light irradiation. Compared with C₆₀/BN-D6 and C₆₀/BN-V6 synthesized under dark and visible-light irradiation, C₆₀/BN-U6 synthesized under UV-light irradiation has the largest adsorption and photodegradation performance for TC under visible-light irradiation. FTIR and XPS characterizations suggest that C₆₀/BN composite is most likely the charge transfer composite, in which C₆₀ acts as electron acceptor and BN acts as electron donor. UV-light has the best promotion effect for the formation of C₆₀/BN. The adsorption quantity of TC by C₆₀/BN-U6 is 2.77 times higher than that of BN (131.05 mg g^-1 vs. 47.27 mg g^-1), being due to that C₆₀/BN-U6 has higher surface area than BN (135.7 m² g^-1 vs. 18.8 m² g^-1). The photodegradation of C₆₀/BN-U6 for TC follows Z-scheme heterojunction mechanism, as well as the photo-induced ·O^2- and h⁺ are the dominant photoactive species. Quantitative structure-activity relationship (QSAR) method is applied to evaluate the toxicity of TC and its photodegradation intermediates. The photodegradation rate of C₆₀/BN-U6 for TC is 19.19 times, 10.06 times, 5.83 times, 2.73 times and 1.84 times higher than that of TiO₂ (P25), g-C₃N₄, BNPA, BCNPA, and BN/TiO₂, respectively, implying that C₆₀/BN-U is a good metal-free photocatalyst.

Electron Precise Sodium Carbaboride Nanocrystals from Molten Salts: Single Sources to Boron Carbides

Boron-rich solids exhibit specific crystal structures and unique properties, which are only very scarcely addressed in nanoparticles. In this work, we address the original inorganic structural chemistry and reactivity of boron-rich nanoparticles, by reporting the first occurrence of sodium carbaboride nanocrystals based on the NaB₅C crystal structure. To design these sub-10 nm nano-objects, we use liquid-phase synthesis in molten salts at 900 °C. By combining a set of characterization tools including powder X-ray powder diffraction, transmission electron microscopy, solid-state nuclear magnetic resonance coupled to DFT modeling, and X-ray photoelectron spectroscopy, we demonstrate that these nanocrystals deviate from the ideal stoichiometry reported for the bulk compound. We suggest that the carbon and sodium contents compensate each other to ensure that the octahedral cluster-based framework is stabilized by fulfilling an electron counting rule. These nanocrystals encompass substituted octahedral covalent structural building units not reported in the related bulk compound. They then shed new light on the ability of nanoparticles to host wide solid solution ranges in covalent solids and then to yield new solids. We finally show that these nanocrystals are efficient single sources of boron and carbon to form a nanostructured boron carbide, thus paving the way to new nanostructured materials.

Photocatalytic hydrogen evolution from biomass conversion

Biomass has incredible potential as an alternative to fossil fuels for energy production that is sustainable for the future of humanity. Hydrogen evolution from photocatalytic biomass conversion not only produces valuable carbon-free energy in the form of molecular hydrogen but also provides an avenue of production for industrially relevant biomass products. This photocatalytic conversion can be realized with efficient, sustainable reaction materials (biomass) and inexhaustible sunlight as the only energy inputs. Reported herein is a general strategy and mechanism for photocatalytic hydrogen evolution from biomass and biomass-derived substrates (including ethanol, glycerol, formic acid, glucose, and polysaccharides). Recent advancements in the synthesis and fundamental physical/mechanistic studies of novel photocatalysts for hydrogen evolution from biomass conversion are summarized. Also summarized are recent advancements in hydrogen evolution efficiency regarding biomass and biomass-derived substrates. Special emphasis is given to methods that utilize unprocessed biomass as a substrate or synthetic photocatalyst material, as the development of such will incur greater benefits towards a sustainable route for the evolution of hydrogen and production of chemical feedstocks.

Recent Developments in the Use of Heterogeneous Semiconductor Photocatalyst Based Materials for a Visible-Light-Induced Water-Splitting System—A Brief Review

Visible-light-driven photoelectrochemical (PEC) and photocatalytic water splitting systems featuring heterogeneous semiconductor photocatalysts (oxynitrides, oxysulfides, organophotocatalysts) signify an environmentally friendly and promising approach for the manufacturing of renewable hydrogen fuel. Semiconducting electrode materials as the main constituents in the PEC water splitting system have substantial effects on the device’s solar-to-hydrogen (STH) conversion efficiency. Given the complication of the photocatalysis and photoelectrolysis methods, it is indispensable to include the different electrocatalytic materials for advancing visible-light-driven water splitting, considered a difficult challenge. Heterogeneous semiconductor-based materials with narrower bandgaps (2.5 to 1.9 eV), equivalent to the theoretical STH efficiencies ranging from 9.3% to 20.9%, are recognized as new types of photoabsorbents to engage as photoelectrodes for PEC water oxidation and have fascinated much consideration. Herein, we spotlight mainly on heterogenous semiconductor-based photoanode materials for PEC water splitting. Different heterogeneous photocatalysts based materials are emphasized in different groups, such as oxynitrides, oxysulfides, and organic solids. Lastly, the design approach and future developments regarding heterogeneous photocatalysts oxide electrodes for PEC applications and photocatalytic applications are also discussed.

Mechanical exfoliation of boron carbide: A metal-free catalyst for aerobic oxidative desulfurization in fuel

Metal-free catalysts have been proved to be a low-cost and environmentally friendly species in aerobic oxidative desulfurization (ODS). In this work, exfoliated metal-free boron carbide with few-layered structure, small size, and abundant defects, was first employed in an aerobic ODS system for ultra-deep desulfurization. The exfoliation process was realized by employing a planetary ball mill strategy. Detailed characterizations showed that the ball milling process not only induces thinner layers and small sizes but also introduces numerous defects into the boron carbide catalysts, which is vital in metal-free catalysis. Furthermore, the exfoliated boron carbide catalyst was applied in aerobic ODS system, and 99.5 % of sulfur removal was obtained. Moreover, the catalyst can be recycled 17 times without a significant decrease in catalytic activity. In particular, it was found that ∼90 % of the sulfur compounds in real diesel oil could be removed by the current aerobic ODS system.

Carbon Sphere Template Derived Hollow Nanostructure for Photocatalysis and Gas Sensing

As a green and preferred technology for energy crisis and environmental issues, continuous research on photocatalysis and gas sensing has come forth at an explosive rate. Thus far, promising synthetic methods have enabled various designs and preparations of semiconductor-based nanostructure which have shown superior activity. This review summarized various synthetic routines toward carbon sphere template derived hollow nanostructures and their successful attempts in synthesize doping, solid solution, heterostructure, and surface modified nanostructures for heterogeneous photocatalysis and gas sensing. Moreover, the challenges and future prospects are briefly discussed. It is eagerly anticipated that this review may broaden the view and in-depth understanding of carbon sphere template derived hollow nanostructures while expected to have further progresses in heterogeneous photocatalysis, gas sensing and other related fields which will make great contributions to their application.

Visible light driven CuBi2O4/Bi2MoO6 p-n heterojunction with enhanced photocatalytic inactivation of E. coli and mechanism insight

Here, a novel CuBi₂O₄/Bi₂MoO₆ (CBO/BMO) p-n heterojunction was fabricated and exhibited markedly improved photocatalytic inactivation capacity of E. coli cells under visible light excitation (λ > 420 nm) compared with pure CuBi₂O₄ and Bi₂MoO₆. The CBO/BMO-0.5 hybrid displayed the highest photoinactivation ability which could completely inactivate the E. coli cellswithin 4 h. The mechanism of photocatalytic disinfection towards E. coli of CBO/BMO heterojunctions was attributed to the disruption of cell-membrane, leakage and damage of cellular content including total protein and DNA as verified with SEM, fluorescence-base dead/live stain, sodium dodecyl sulfate polyacrylamide gel electropheresis (SDS-PAGE) and agarose gel electrophoresis (AGE). Additionally, the scavenge experiments showed that the reactive species h⁺, e^- and •O_2^-play the predominant role in the photocatalytic system of CBO/BMO hybrids. The improved photocatalytic activity of CBO/BMO composites was mainly attributed to the promotion of spatial separation and migration rate of photoproduced electron-hole pairs, enhancement of visible light absorption and more generation of reactive species (•O₂^-) on the interface of catalyst and water which was demonstrated by nitroblue tetrazolium (NBT) and EPR. Our work indicated that construction of CuBi₂O₄/Bi₂MoO₆ p-n heterostructure photocatalyst is a promising environmental friendly alternative method to deal with the biohazards of pathogenic microorganisms.

Metal-free photocatalysts for hydrogen evolution

This article provides a comprehensive review of the latest progress, challenges and recommended future research related to metal-free photocatalysts for hydrogen productionviawater-splitting.

Isoelectronic analogues of graphene: the BCN monolayers with visible-light absorption and high carrier mobility

By employing particle-swarm optimization (PSO) and first-principles computations, we theoretically predicted five stable phases of graphene-like borocarbonitrides (g-BCN) with the stoichiometric ratio of 1:1:1 and uniformly distributed B, C, N atoms, which are the isoelectronic analogues of graphene. These g-BCN monolayers are effectively stabilized by their relatively high proportion of robust C-C or B-N bonds and strong partial ionic-covalent B-C and C-N bonds within them, leading to pronounced thermal and kinetic stability. The visible-light absorption and high carrier mobility of the investigated g-BCN monolayers indicate their possible applications in high-efficiency photochemical processes and electronic devices. Our computations could provide some guidance for designing the graphene-like materials with earth-abundant elements, as well as some clues for the experimental synthesis and practical applications of ternary BCN nanosheets.

Borocarbonitrides as Metal-Free Catalysts for the Hydrogen Evolution Reaction

Hydrogen generation by water splitting is clearly a predominant and essential strategy to tackle the problems related to renewable energy. In this context, the discovery of proper catalysts for electrochemical and photochemical water splitting assumes great importance. There is also a serious intent to eliminate platinum and other noble metal catalysts. To replace Pt by a non-metallic catalyst with desirable characteristics is a challenge. Borocarbonitrides, (B_x C_y N_z ) which constitutes a new class of 2D material, offer great promise as non-metallic catalysts because of the easy tunability of bandgap, surface area, and other electronic properties with variation in composition. Recently, B_x C_y N_z composites with excellent electrochemical and photochemical hydrogen generation activities have been found, especially noteworthy being the observation that B_x C_y N_z with a carbon-rich composition or its nanocomposites with MoS₂ come close to Pt in electrocatalytic properties, showing equally good photochemical activity.

Computational discovery and characterization of new B2O phases

We present computational discoveries of new structural phases of the B2O compound exhibiting novel bonding networks and electronic states at ambient and elevated pressures. Our advanced crystal structure searches in conjunction with density functional theory calculations have identified an orthorhombic phase of B2O that is energetically stable at ambient pressure and contains an intriguing bonding network of icosahedral B12 clusters bridged by oxygen atoms. As pressure increases above 1.9 GPa, a structural transformation takes the orthorhombic B2O into a pseudo-layered trigonal phase. We have performed extensive studies to investigate the evolution of chemical bonds and electronic states associated with the B12 icosahedral unit in the orthorhombic phase and the covalent B-O bonds in the trigonal phase. We have also examined the nature of the charge carriers and their coupling to the lattice vibrations in the newly identified B2O crystals. Interestingly, our results indicate that both B2O phases become superconducting at low temperatures, with transition temperatures of 6.4 K and 5.9 K, respectively, in the ambient and high-pressure phase. The present findings establish new B2O phases and characterize their structural and electronic properties, which offer insights and guidance for exploration toward further fundamental understanding and potential synthesis and application.

A carbon-rich nanofiber framework based on a conjugated arylacetylene polymer for photocathodic enzymatic bioanalysis

The metal-free photocathode fabricated by porous carbon-rich nanofiber framework of PTEB film realized “signal-off” photocathodic bioanalysis of glucose.

In Situ-Fabricated 2D/2D Heterojunctions of Ultrathin SiC/Reduced Graphene Oxide Nanosheets for Efficient CO2 Photoreduction with High CH4 Selectivity

Photoreduction of CO₂ into fuel molecules such as CH₄ represents a promising route to simultaneously explore renewable energy and alleviate global warming. However, the implementation of such a process is hampered by low product yields and poor selectivity. A 2D/2D heterojunction of ultrathin SiC and reduced graphene oxide (RGO) nanosheets was fabricated in situ for efficient and selective photoreduction of CO₂ . Ultrathin SiC suppresses significant charge recombination in the bulk phase, thus providing more energetic electrons. The robust 2D/2D heterojunction allows fast transfer of energetic electrons from SiC to RGO. Combining the vital role of RGO in facilitating CO₂ activation, the optimized SiC/RGO exhibits an electron-transfer rate of 58.17 μmol h^-1  g^-1 towards CO₂ reduction, 2.7 times that of pure SiC (20.25 μmol h^-1  g^-1 ). About 92 % of the transferred electrons from SiC are devoted to generating CH₄ (6.72 μmol h^-1  g^-1 ). Such high efficiency and selectivity are mainly a result of the densely accumulated energetic electrons within RGO, which facilitate the eight-electron process to produce CH₄ . This work will inspire the design of catalyst/cocatalyst systems for efficient and selective photoreduction of CO₂ .

Electronic and Optical Properties of 2D Materials Constructed from Light Atoms

Boron, carbon, nitrogen, and oxygen atoms can form various building blocks for further construction of structurally well-defined 2D materials (2DMs). Both in theory and experiment, it has been documented that the electronic structures and optical properties of 2DMs are well tunable through a rational design of the material structure. Here, the recent progress on 2DMs that are composed of B, C, N, and O elements is introduced, including borophene, graphene, h-BN, g-C₃ N₄ , organic 2D polymers (2DPs), etc. Attention is put on the band structure/bandgap engineering for these materials through a variety of methodologies, such as chemical modifications, layer number and atomic structure control, change of conjugation degree, etc. The optical properties, such as photoluminescence, thermoluminescence, single photon emission, as well as the associated applications in bioimaging and sensing, are discussed in detail and highlighted.

Theoretical Studies on the Electronic and Optical Properties of Honeycomb BC3 monolayer: A Promising Candidate for Metal-free Photocatalysts

By employing first-principles computations and particle-swarm optimization calculations, we theoretically confirmed the honeycomb geometry of experimentally realized BC3 sheet, which is constructed by the hexagonal carbon-ring fragments surrounded by six boron atoms and has pronounced thermodynamic stabilities. Remarkably, the computations also demonstrate the visible-light absorption, high carrier mobilities, and promising reduction and oxidation capacities of the BC3 monolayer, indicating its efficient absorption of solar radiation, fast migration of electron and holes, and excellent capabilities of photoinduced carriers in a photocatalytic process, respectively. Additionally, its indirect band gap, spatially separated charge distributions, and great difference in mobilities of electrons and holes should lead to the restricted recombination of photoactivated e--h+ pairs within BC3 monolayer. All above-mentioned characteristics suggest that the honeycomb BC3 monolayer should be a recommendable candidate for metal-free photocatalysts, which is worthy of further verifications and explorations in experimental studies.

Origin and Perspectives of the Photochemical Activity of Nanoporous Carbons

Even though, owing to the complexity of nanoporous carbons' structure and chemistry, the origin of their photoactivity is not yet fully understood, the recent works addressed here clearly show the ability of these materials to absorb light and convert the photogenerated charge carriers into chemical reactions. In many aspects, nanoporous carbons are similar to graphene; their pores are built of distorted graphene layers and defects that arise from their amorphicity and reactivity. As in graphene, the photoactivity of nanoporous carbons is linked to their semiconducting, optical, and electronic properties, defined by the composition and structural defects in the distorted graphene layers that facilitate the exciton splitting and charge separation, minimizing surface recombination. The tight confinement in the nanopores is critical to avoid surface charge recombination and to obtain high photochemical quantum yields. The results obtained so far, although the field is still in its infancy, leave no doubts on the possibilities of applying photochemistry in the confined space of carbon pores in various strategic disciplines such as degradation of pollutants, solar water splitting, or CO2 mitigation. Perhaps the future of photovoltaics and smart-self-cleaning or photocorrosion coatings is in exploring the use of nanoporous carbons.

Heterogeneous photocatalysis and its potential applications in water and wastewater treatment: a review

There has been a considerable amount of research in the development of sustainable water treatment techniques capable of improving the quality of water. Unavailability of drinkable water is a crucial issue especially in regions where conventional drinking water treatment systems fail to eradicate aquatic pathogens, toxic metal ions and industrial waste. The research and development in this area have given rise to a new class of processes called advanced oxidation processes, particularly in the form of heterogeneous photocatalysis, which converts photon energy into chemical energy. Advances in nanotechnology have improved the ability to develop and specifically tailor the properties of photocatalytic materials used in this area. This paper discusses many of those photocatalytic nanomaterials, both metal-based and metal-free, which have been studied for water and waste water purification and treatment in recent years. It also discusses the design and performance of the recently studied photocatalytic reactors, along with the recent advancements in the visible-light photocatalysis. Additionally, the effects of the fundamental parameters such as temperature, pH, catalyst-loading and reaction time have also been reviewed. Moreover, different techniques that can increase the photocatalytic efficiency as well as recyclability have been systematically presented, followed by a discussion on the photocatalytic treatment of actual wastewater samples and the future challenges associated with it.

Copper-surface-mediated synthesis of acetylenic carbon-rich nanofibers for active metal-free photocathodes

The engineering of acetylenic carbon-rich nanostructures has great potential in many applications, such as nanoelectronics, chemical sensors, energy storage, and conversion, etc. Here we show the synthesis of acetylenic carbon-rich nanofibers via copper-surface-mediated Glaser polycondensation of 1,3,5-triethynylbenzene on a variety of conducting (e.g., copper, graphite, fluorine-doped tin oxide, and titanium) and non-conducting (e.g., Kapton, glass, and silicon dioxide) substrates. The obtained nanofibers (with optical bandgap of 2.51 eV) exhibit photocatalytic activity in photoelectrochemical cells, yielding saturated cathodic photocurrent of ca. 10 µA cm-2 (0.3-0 V vs. reversible hydrogen electrode). By incorporating thieno[3,2-b]thiophene units into the nanofibers, a redshift (ca. 100 nm) of light absorption edge and twofold of the photocurrent are achieved, rivalling those of state-of-the-art metal-free photocathodes (e.g., graphitic carbon nitride of 0.1-1 µA cm-2). This work highlights the promise of utilizing acetylenic carbon-rich materials as efficient and sustainable photocathodes for water reduction.

Superstructure Ta2O5 mesocrystals derived from (NH4)2Ta2O3F6 mesocrystals with efficient photocatalytic activity

Superstructured mesocrystalline Ta₂O₅ nanosheets were successfully prepared from mesocrystalline (NH₄)₂Ta₂O₃F₆ nanorods by the annealing method.

Solvothermal synthesis and enhanced photo-electrochemical performance of hierarchically structured strontium titanate micro-particles

Homogeneous powders of almost spherical particles of SrTiO₃ with diameters of about 1 μm and large surface areas of up to 186 m² g⁻¹ were obtained from a facile one-pot solvothermal synthesis.

Nanomaterials for photocatalytic hydrogen production: from theoretical perspectives

To overcome the increasing demand of energy worldwide and global warming due to CO₂emissions from the use of traditional fuel sources, renewable and clean energy sources are in high demand.

Bio-templated fabrication of metal-free boron carbonitride tubes for visible light photocatalysis

A novel and facile biotemplating method has been presented to synthesize boron carbon nitride tubes (BCNTs) by using the low-cost kapok fibers (KFs). This pathway not only transplanted the structure of KFs into the h-BN lattice, but also introduced C simultaneously in a self-doping manner. The BCNT photocatalysts can catalyse hydrogen evolution from water under visible light illumination.

Disorder and defects are not intrinsic to boron carbide

A unique combination of useful properties in boron-carbide, such as extreme hardness, excellent fracture toughness, a low density, a high melting point, thermoelectricity, semi-conducting behavior, catalytic activity and a remarkably good chemical stability, makes it an ideal material for a wide range of technological applications. Explaining these properties in terms of chemical bonding has remained a major challenge in boron chemistry. Here we report the synthesis of fully ordered, stoichiometric boron-carbide B13C2 by high-pressure-high-temperature techniques. Our experimental electron-density study using high-resolution single-crystal synchrotron X-ray diffraction data conclusively demonstrates that disorder and defects are not intrinsic to boron carbide, contrary to what was hitherto supposed. A detailed analysis of the electron density distribution reveals charge transfer between structural units in B13C2 and a new type of electron-deficient bond with formally unpaired electrons on the C-B-C group in B13C2. Unprecedented bonding features contribute to the fundamental chemistry and materials science of boron compounds that is of great interest for understanding structure-property relationships and development of novel functional materials.

Inorganic perovskite photocatalysts for solar energy utilization

This review specifically summarizes the recent development of perovskite photocatalysts and their applications in water splitting and environmental remediation.

Recent advances in non-metal modification of graphitic carbon nitride for photocatalysis: a historic review

This review provides a comprehensive survey and critical comments on the development of photocatalysts with a focus on the metal-free materials.

Metal-free carbonaceous electrocatalysts and photocatalysts for water splitting

This tutorial review focuses on the recent progress in the development of metal-free carbonaceous electrocatalysts and photocatalysts for hydrogen and/or oxygen evolution from water.

Carbon-doped BN nanosheets for metal-free photoredox catalysis

The generation of sustainable and stable semiconductors for solar energy conversion by photoredox catalysis, for example, light-induced water splitting and carbon dioxide reduction, is a key challenge of modern materials chemistry. Here we present a simple synthesis of a ternary semiconductor, boron carbon nitride, and show that it can catalyse hydrogen or oxygen evolution from water as well as carbon dioxide reduction under visible light illumination. The ternary B–C–N alloy features a delocalized two-dimensional electron system with sp² carbon incorporated in the h-BN lattice where the bandgap can be adjusted by the amount of incorporated carbon to produce unique functions. Such sustainable photocatalysts made of lightweight elements facilitate the innovative construction of photoredox cascades to utilize solar energy for chemical conversion.

Metal-free semiconductors with appropriate bandgaps create photocatalytic routes to water splitting and CO₂ reduction. Here the authors dope hexagonal boron nitride nanosheets with carbon via a simple method to synthesize a ternary B–C–N alloy capable of performing just this function.

Cadmium sulfide quantum dots stabilized by aromatic amino acids for visible light-induced photocatalytic degradation of organic dyes

CdS QDs stabilized by aromatic amino acids photocatalytically degrade organic dyes under visible light irradiation through mediation of hydroxyl radicals.