Enhanced visible-light photocatalytic activity of g-C3N4/Zn2GeO4 heterojunctions with effective interfaces based on band match

Serpentine Ni3 Ge2 O5 (OH)4 Nanosheets with Tailored Layers and Size for Efficient Oxygen Evolution Reactions

Layered serpentine Ni₃ Ge₂ O₅ (OH)₄ is compositionally active and structurally favorable for adsorption and diffusion of reactants in oxygen evolution reactions (OER). However, one of the major problems for these materials is limited active sites and low efficiency for OER. In this regard, a new catalyst consisting of layered serpentine Ni₃ Ge₂ O₅ (OH)₄ nanosheets is introduced via a controlled one-step synthetic process where the morphology, size, and layers are well tailored. The theoretical calculations indicate that decreased layers and increased exposure of (100) facets in serpentine Ni₃ Ge₂ O₅ (OH)₄ lead to much lower Gibbs free energy in adsorption of reactive intermediates. Experimentally, it is found that the reduction in number of layers with minimized particle size exhibits plenty of highly surface-active sites of (100) facets and demonstrates a much enhanced performance in OER than the corresponding multilayered nanosheets. Such a strategy of tailoring active sites of serpentine Ni₃ Ge₂ O₅ (OH)₄ nanosheets offers an effective method to design highly efficient electrocatalysts.

Enhanced Visible-Light-Driven Photocatalytic Bacterial Inactivation by Ultrathin Carbon-Coated Magnetic Cobalt Ferrite Nanoparticles

Ultrathin hydrothermal carbonation carbon (HTCC)-coated cobalt ferrite (CoFe₂O₄) composites with HTCC coating thicknesses between 0.62 and 4.38 nm were fabricated as novel, efficient, and magnetically recyclable photocatalysts via a facile, green approach. The CoFe₂O₄/HTCC composites showed high magnetization and low coercivity, which favored magnetic separation for reuse. The results show that the close coating of HTCC on CoFe₂O₄ nanoparticles enhanced electron transfer and charge separation, leading to a significant improvement in photocatalytic efficiency. The composites exhibited superior photocatalytic inactivation toward Escherichia coli K-12 under visible-light irradiation, with the complete inactivation of 7 log₁₀ cfu·mL^-1 of bacterial cells within 60 min. The destruction of bacterial cell membranes was monitored by field-effect scanning electron microscopy analysis and fluorescence microscopic images. The bacterial inactivation mechanism was investigated in a scavenger study, and ^•O₂, H₂O₂, and h⁺ were identified as the major reactive species for bacterial inactivation. Multiple cycle runs revealed that these composites had excellent stability and reusability. In addition, the composites showed good photocatalytic bacterial inactivation performance in authentic water matrices such as surface water samples and secondarily treated sewage effluents. The results of this work indicate that CoFe₂O₄/HTCC composites have great potential in large-scale photocatalytic disinfection operations.

Quasi-polymeric construction of stable perovskite-type LaFeO3/g-C3N4 heterostructured photocatalyst for improved Z-scheme photocatalytic activity via solid p-n heterojunction interfacial effect

Materials of perovskite-type structure have attracted considerable attention for their applications in photocatalysis. In this study, a novel composite of p-type LaFeO₃ microsphere coated with n-type nanosized graphitic carbon nitride nanosheets was constructed by the quasi-polymeric calcination method with the aid of electrostatic self-assembly interaction. Results indicate that the LaFeO₃/g-C₃N₄p-n heterostructured photocatalyst obtained, in contrast to the pure constituents, enabled improved visible-light absorption, and more efficient separation and migration of charge carriers via solid p-n heterojunction interfacial effect. Correspondingly, the LaFeO₃/g-C₃N₄ composite allowed for higher visible-light-responsive photocatalytic activity for the degradation of Brilliant Blue, which was 16.9 and 7.8 times that of pristine g-C₃N₄ and LaFeO₃, respectively. The photocatalytic degradation of Brilliant Blue was ascribed to the combined contributions of the photogenerated holes (h⁺), superoxide radicals (O₂^-) and hydroxyl radicals (OH). Based on solid p-n heterojunction interfacial interaction, a Z-scheme charge carrier transfer pathway integrated with the dye-sensitization effect is proposed as the underlying mechanism of the photocatalytic reaction process. Therefore, we believe that the perovskite-type LaFeO₃/g-C₃N₄ Z-scheme photcatalyst promotes the development of photocatalysis and holds much promise for environmental remediation.

A novel efficient g-C3N4@BiOI p–n heterojunction photocatalyst constructed through the assembly of g-C3N4 nanoparticles

A novel g-C₃N₄@BiOI p–n surficial dispersive heterojunction photocatalyst was constructed by simply loading g-C₃N₄ nanoparticles on flower-like BiOI nanosheets.

Hydrothermal synthesis of Bi2WO6 with a new tungsten source and enhanced photocatalytic activity of Bi2WO6 hybridized with C3N4

Photogenerated holes of Bi₂WO₆ transfer to the highest occupied molecular orbital of C₃N₄, causing a reduction of e⁻/h⁺ recombination.

Preparation of phenyl group functionalized g-C3N4 nanosheets with extended electron delocalization for enhanced visible-light photocatalytic activity

Phenyl group functionalized g-C₃N₄ shows an improved light utilization and charges separation rate due to extended conjugation system, leading to a superior catalytic activity in a variety of photocatalytic systems.

Charge transport, interfacial interactions and synergistic mechanisms in BiNbO4/MWO4 (M = Zn and Cd) heterostructures for hydrogen production: insights from a DFT+U study

In the 21st century, the growing demand of global energy is one of the key challenges. The photocatalytic generation of hydrogen has attracted extensive attention to discuss the increasing global demand for sustainable and clean energy. However, hydrogen evolution reactions normally use the economically expensive rare noble metals and the processes remain a challenge. Herein, low-cost BiNbO₄/MWO₄(010) heterostructures are studied for the first time to check their suitability towards photocatalytic hydrogen production. A theoretical study with the aid of density functional theory (DFT) is used to investigate the synergistic effect, ionisation energy, electron affinities, charge transfer, electronic properties and the underlying mechanism for hydrogen generation of BiNbO₄/MWO₄(010) heterostructures. The experimental band gaps of bulk ZnWO₄, CdWO₄ and BiNbO₄ are well reproduced using the DFT+U method. The calculated band edge position shows a type-II staggered band alignment and the charge transfer between BiNbO₄ and MWO₄ monolayers results in a large interfacial built-in potential, which will favour the separation of charge carriers in the heterostructures. The effective mass of the photoinduced holes is higher compared to the electrons, making the heterostructures useful in hydrogen production. The relatively low ionisation energy and electron affinity for the heterostructures compared to the monolayers make them ideal for photocatalysis applications due to their small energy barrier for the injection of electrons and creation of holes. The BiNbO₄/MWO₄(010) heterostructures are more suitable for photocatalytic hydrogen production due to their strong reducing power relative to the H⁺/H₂O potential. This study sheds light on the less known BiNbO₄/ZnWO₄(010) heterostructures and the fully explored electronic and optical properties will pave way for future photocatalytic water splitting applications.

Enhanced photo-electrochemical response of reduced graphene oxide and C3N4 nanosheets for rutin detection

Herein, a sensitive photo-electrochemical sensor based on C₃N₄ and reduced graphene oxide nanosheets modified glassy carbon electrode (C₃N₄-RGO/GCE) has been fabricated for the detection of rutin under UV light illumination. In C₃N₄-RGO catalyst, RGO not only works as a template but also promotes electron transfer, meanwhile, C₃N₄ acts as a photocatalyst. Benefiting from the superior electron transfer capacity and efficient UV light effect of the C₃N₄-RGO catalyst, we get a photo-electrochemical sensor for the rutin detecting with a low detection limit of 1.78×10^-9molL^-1 and an excellent linear range of 5×10^-9-1.4×10^-4molL^-1. Meanwhile, the achieved C₃N₄-RGO/GCE demonstrated nice selectivity, good reproducibility as well as reliable stability. Moreover, compared with the electrochemical determination, the C₃N₄-RGO electrode provides a new way for rutin detection by photo-electrochemical method with a promising UV light responsive result.

Understanding the mechanism of enhanced charge separation and visible light photocatalytic activity of modified wurtzite ZnO with nanoclusters of ZnS and graphene oxide: from a hybrid density functional study

A hybrid ternary ZnS/GO/ZnO(001) system achieved enough driving force for splitting water into H₂ gas.

Boron-doped graphitic carbon nitride nanosheets for enhanced visible light photocatalytic water splitting

A new type of boron-doped graphitic carbon nitride (B-g-C₃N₄) nanosheets was prepared by a benign one-pot thermal polycondensation process.

Superior photocatalytic performance of LaFeO3/g-C3N4 heterojunction nanocomposites under visible light irradiation

New type of Z-scheme LaFeO₃/g-C₃N₄ heterostructures were successfully prepared and the enhanced photocatalytic hydrogen evolution and degradation activities are presented.

Rational fabrication of a graphitic-C3N4/Sr2KNb5O15 nanorod composite with enhanced visible-light photoactivity for degradation of methylene blue and hydrogen production

Formation of proper interfaces between g-C₃N₄ and Sr₂KNb₅O₁₅ by direct growth approach greatly enhanced the photodegradation and hydrogen production activity.

Photocatalytic hydrogen evolution performance of NiS cocatalyst modified LaFeO3/g-C3N4 heterojunctions

NiS cocatalyst modified LaFeO₃/g-C₃N₄ heterostructures were prepared and their enhanced photocatalytic hydrogen evolution performance under visible light irradiation was presented.

A Facile Method to In-Situ Synthesize Porous Ni₂GeO₄ Nano-Sheets on Nickel Foam as Advanced Anode Electrodes for Li-Ion Batteries

A strategy for growth of porous Ni₂GeO₄ nanosheets on conductive nickel (Ni) foam with robust adhesion as a high-performance electrode for Li-ion batteries is proposed and realized, through a facile two-step method. It involves the low temperature hydro-thermal synthesis of bimetallic (Ni, Ge) hydroxide nanosheets precursor on Ni foam substrates and subsequent thermal transformation to porous Ni₂GeO₄ nanosheets. The as-prepared Ni₂GeO₄ nanosheets possess many interparticle mesopores with a size range from 5 to 15 nm. The hierarchical structure of porous Ni₂GeO₄ nanosheets supported by Ni foam promises fast electron and ion transport, large electroactive surface area, and excellent structural stability. The efficacy of the specially designed structure is demonstrated by the superior electrochemical performance of the generated Ni₂GeO₄ nanosheets including a high capacity of 1.8 mA·h·cm^-2 at a current density of 50 μA·cm^-2, good cycle stability, and high power capability at room temperature. Because of simple conditions, this fabrication strategy may be easily extended to other mixed metal oxides (M_xGeO_y).

Fabrication of CoTiO3/g-C3N4 Hybrid Photocatalysts with Enhanced H2 Evolution: Z-Scheme Photocatalytic Mechanism Insight

A novel direct Z-scheme CoTiO3/g-C3N4 (CT-U) photocatalytic system with different weight percentage of CoTiO3 was synthesized using a facile in situ growth method for H2 evolution from water splitting. The as-prepared CT-U composites composed of 1D CoTiO3 microrod and 2D g-C3N4 nanosheet were characterized by various techniques including XRD, SEM, TEM, XPS, FTIR, and UV-vis. Results demonstrate that the CT-U composite photocatalysts were successfully fabricated, with intimate interfacial contact and heterojunction interaction between g-C3N4 and CoTiO3 which can significantly boost the photocatalytic activity compared with prinstine g-C3N4 and CoTiO3. The most enhanced H2-evolution rate of 858 μmol h(-1) g(-1) and high quantum efficiency (38.4% at 365 nm, 3.23% at 420 ± 20 nm) are achieved at an optimal 0.15% CT-U. Meanwhile, the 0.15% CT-U sample exhibits good photocatalytic stability in recycling H2 evolution. Accordingly, direct Z-scheme mechanism capable of leading efficient charge carrier separation and strong reduction ability for enhanced H2 production was proposed, and further evidenced by PL, photoelectrochemical analysis, and ESR assay.

Flower-like N-doped MoS2 for photocatalytic degradation of RhB by visible light irradiation

In this paper, the photocatalytic performance and reusability of N-doped MoS2 nanoflowers with the specific surface area of 114.2 m(2) g(-1) was evaluated by discoloring of RhB under visible light irradiation. Results indicated that the 20 mg fabricated catalyst could completely degrade 50 ml of 30 mg l(-1) RhB in 70 min with excellent recycling and structural stability. The optimized N-doped MoS2 nanoflowers showed a reaction rate constant (k) as high as 0.06928 min(-1) which was 26.4 times that of bare MoS2 nanosheets (k = 0.00262). In addition, it was about seven times that of P25 (k = 0.01) (Hou et al 2015 Sci. Rep. 5 15228). The obtained outstanding photocatalytic performance of N-doped MoS2 nanoflowers provides potential applications in water pollution treatment, as well as other related fields.

Synthesis of a SrFeO3−x/g-C3N4heterojunction with improved visible-light photocatalytic activities in chloramphenicol and crystal violet degradation

Some solid magnetic photocatalysts containing ferrites are convenient for being separated from reaction solutions by a magnet.

A novel heterojunction photocatalyst, Bi2SiO5/g-C3N4: synthesis, characterization, photocatalytic activity, and mechanism

A new type of heterojunction photocatalyst, Bi₂SiO₅/g-C₃N₄, was prepared using a controlled hydrothermal method.

Efficient degradation of organic pollutants and hydrogen evolution by g-C3N4 using melamine as the precursor and urea as the modifier

A novel metal-free photocatalyst g-C₃N₄/g-C₃N₄ isotypeheterojunction has been successfully fabricated. More importantly, the as-obtained material exhibits remarkable enhanced photocatalytic properties owing to the designed visible-light bandgap and band edges..

Zn2−aGeO4:aRE and Zn2Ge1−aO4:aRE (RE = Ce3+, Eu3+, Tb3+, Dy3+): 4f–4f and 5d–4f transition luminescence of rare earth ions under different substitution

Generally, luminescent properties of rare earth ions doped host can be tuned by controlling the host composition, that is, when substituted for different cations of host, the rare earths ions can present different characteristics.

Construction of a 2D/2D g-C3N4/rGO hybrid heterojunction catalyst with outstanding charge separation ability and nitrogen photofixation performance via a surface protonation process

Heterojunction catalyst PCN/rGO with effective interfacial contact by incorporating reduced graphene oxide and protonated g-C₃N₄ and outstanding nitrogen photofixation ability was synthesized via a electrostatic self-assembly strategy.

Exploring the effects of nanocrystal facet orientations in g-C₃N₄/BiOCl heterostructures on photocatalytic performance

Effective separation and migration of photogenerated electron-hole pairs are two key factors to determine the performance of photocatalysts. It has been widely accepted that photocatalysts with heterojunctions usually exhibit excellent charge separation. However, the migration process of separated charges in the heterojunction structures has not been fully investigated. Herein, photocatalysts with heterojunctions are constructed by loading g-C3N4 nanoparticles onto BiOCl nanosheets with different exposed facets (BOC-001 and BOC-010). The g-C3N4 nanoparticles with decreasing size and increasing zeta potential could induce stronger coupling and scattering in the heterojunction. The relationship between the crystal facet orientation in the BiOCl nanosheets and charge separation/effective migration behaviours of the materials is investigated. The visible light photocatalytic activity of the composites is evaluated by methyl orange (MO) and phenol degradation experiments, and the results show that ng-CN/BOC-010 composites exhibit higher photocatalytic performance than that of ng-CN/BOC-001 composites. Both photoelectrochemical and fluorescence emission measurements indicate that the different exposed facets in ng-CN/BiOCl composites could induce the migration of the photogenerated electrons in different ways, but do not significantly alter the separation efficiencies. The separated electrons in ng-CN/BOC-010 undergo a shorter transport distance than that of ng-CN/BOC-001 to reach the surface reactive sites. The study may suggest that the crystal facet orientation in polar semiconductors is a critical factor for designing highly efficient heterojunction photocatalysts.

A facile method of activating graphitic carbon nitride for enhanced photocatalytic activity

Activated graphitic carbon nitride (g-C3N4) with enhanced photocatalytic capability under visible light irradiation was fabricated by using a facile chemical activation treatment method. In the chemical activation, a mixed solution of hydrogen peroxide and ammonia was employed. The yield can reach as high as 90% after the activation process. The activation process did not change the crystal structure, functional group, morphology and specific surface area of pristine g-C3N4, but it introduced H and O elements into the CN framework of g-C3N4, resulting in a broader optical absorption range, higher light absorption capability and more efficient separation of photogenerated electrons and holes. The photoactivity was investigated by the degradation of rhodamine B (RhB) under visible light irradiation. As compared to the pristine g-C3N4, the activated g-C3N4 exhibited a distinct and efficient two-step degradation process. It was found that the RhB dye in the activated g-C3N4 was mainly oxidized by the photogenerated holes. It is believed that sufficient holes account for the two-step degradation process because they would significantly improve the efficiency of the N-de-ethylation reaction of RhB.

Magnetic core-shell CuFe2O4@C3N4 hybrids for visible light photocatalysis of Orange II

Novel CuFe2O4@C3N4 core-shell photocatalysts were fabricated through a self-assembly method and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, transmission electron microscopy and Uv-vis diffuse reflection spectroscopy. The photocatalytic performances of the CuFe2O4@C3N4 catalysts were evaluated in photo Fenton-like discoloration of Orange II dye using H2O2 as an oxidant under visible-light irradiation (λ>420 nm). It was found the CuFe2O4@C3N4 hybrid (mass ratio of CuFe2O4/g-C3N4 at 2:1) exhibits a superior activity as compared with single component of CuFe2O4 or g-C3N4 and the mixture of g-C3N4 and CuFe2O4, due to the elevation of the separation efficiency of photoinduced electron-hole pairs, resulted from the heterojunction between the interfaces of g-C3N4 and CuFe2O4. The quenching tests of different scavengers displayed that O2(•-), OH and h(+) are responsible for the Orange II decolorization. In addition, the effects of initial concentration of the dye contaminant (0.014-0.140 mM), different anions (Cl(-), SO4(2-), NO3(-), CH3COO(-) and HCO3(-)) and temperature (15-65 °C) in photoreaction were also investigated. The CuFe2O4@C3N4 sample exhibited stable performance without obvious loss of catalytic activity after five successive runs, showing a promising application for the photo-oxidative degradation of environmental contaminants.

Two-Dimensional CaIn₂S₄/g-C₃N₄ Heterojunction Nanocomposite with Enhanced Visible-Light Photocatalytic Activities: Interfacial Engineering and Mechanism Insight

Design and exploitation of efficient visible light photocatalytic systems for water splitting and degradation of organic dyes are of huge interest in the fields of energy conversion and environmental protection. Herein, two-dimensional CaIn2S4/g-C3N4 heterojunction nanocomposites with intimate interfacial contact have been synthesized by a facile two-step method. Compared with pristine g-C3N4 and CaIn2S4, the CaIn2S4/g-C3N4 heterojunction nanocomposites exhibited significantly enhanced H2 evolution and photocatalytic degradation of methyl orange (MO) activities under visible light irradiation. The optimal CaIn2S4/g-C3N4 nanocomposite shows a H2 evolution rate of 102 μmol g(-1) h(-1), which is more than 3 times that of pristine CaIn2S4. The mechanisms for improving the photocatalytic performance of the CaIn2S4/g-C3N4 nanocomposites were proposed by using the photoluminescence measurement and electrochemical analyses. It was demonstrated that the enhanced photocatalytic performance of CaIn2S4/g-C3N4 heterojunction nanocomposites mainly stems from the enhanced charge separation efficiency. In addition, a plausible mechanism for the degradation of MO dye over CaIn2S4/g-C3N4 nanocomposites is also elucidated using active species scavenger's studies.

Polymeric photocatalysts based on graphitic carbon nitride

Semiconductor-based photocatalysis is considered to be an attractive way for solving the worldwide energy shortage and environmental pollution issues. Since the pioneering work in 2009 on graphitic carbon nitride (g-C3N4) for visible-light photocatalytic water splitting, g-C3N4 -based photocatalysis has become a very hot research topic. This review summarizes the recent progress regarding the design and preparation of g-C3N4 -based photocatalysts, including the fabrication and nanostructure design of pristine g-C3N4 , bandgap engineering through atomic-level doping and molecular-level modification, and the preparation of g-C3N4 -based semiconductor composites. Also, the photo-catalytic applications of g-C3N4 -based photocatalysts in the fields of water splitting, CO2 reduction, pollutant degradation, organic syntheses, and bacterial disinfection are reviewed, with emphasis on photocatalysis promoted by carbon materials, non-noble-metal cocatalysts, and Z-scheme heterojunctions. Finally, the concluding remarks are presented and some perspectives regarding the future development of g-C3N4 -based photocatalysts are highlighted.

Water-assisted production of honeycomb-like g-C3N4 with ultralong carrier lifetime and outstanding photocatalytic activity

Graphitic carbon nitride (g-C3N4) is a visible light photocatalyst, limited by low activity mainly caused by rapid recombination of charge carriers. In the present work, honeycomb-like g-C3N4 was synthesized via thermal condensation of urea with addition of water at 450 °C for 1 h. Prolonging the condensation time caused the morphology of g-C3N4 to change from a porous honeycomb structure to a velvet-like nanoarchitecture. Unlike in previous studies, the photocatalytic activity of g-C3N4 decreased with increasing surface area. The honeycomb-like g-C3N4 with a relatively low surface area showed highly enhanced photocatalytic activity with an NO removal ratio of 48%. The evolution of NO2 intermediate was dramatically inhibited over the honeycomb-like g-C3N4. The short and long lifetimes of the charge carriers for honeycomb-like g-C3N4 were unprecedentedly prolonged to 22.3 and 165.4 ns, respectively. As a result, the honeycomb-like g-C3N4 was highly efficient and stable in activity and could be used repeatedly. Addition of water had the following multiple positive effects on g-C3N4: (1) formation of the honeycomb structure, (2) promotion of charge separation and migration, (3) enlargement of the band gap, (4) increase in production yield, and (5) decrease in energy cost. These advantages make the present preparation method for highly efficient g-C3N4 extremely appealing for large-scale applications. The active species produced from g-C3N4 under illumination were confirmed using DMPO-ESR spin-trapping, the reaction intermediate was monitored, and the reaction mechanism of photocatalytic NO oxidation by g-C3N4 was revealed. This work could provide an attractive alternative method for mass-production of highly active g-C3N4-based photocatalysts for environmental and energetic applications.

Heterojunction engineering of graphitic carbon nitride (g-C3N4) via Pt loading with improved daylight-induced photocatalytic reduction of carbon dioxide to methane

The Pt-loaded g-C₃N₄ demonstrated high visible-light photoactivity of CO₂ reduction to CH₄, which was attributed to the efficient interfacial electron transfer from g-C₃N₄ to Pt.

The sulfur-bubble template-mediated synthesis of uniform porous g-C3N4 with superior photocatalytic performance

Uniform porous sulfur-mediated g-C₃N₄ has been obtained using a facile sulfur-bubble template-mediated approach and exhibits superior photocatalytic performance.

Synthesis of Bi2Sn2O7 and enhanced photocatalytic activity of Bi2Sn2O7 hybridized with C3N4

The enhanced photocatalytic activity of the C₃N₄/Bi₂Sn₂O₇ photocatalysts could be attributed to the effective separation of the photogenerated e⁻/h⁺ pairs.

Self-assembled synthesis of hierarchical Zn2GeO4 core–shell microspheres with enhanced photocatalytic activity

Hierarchical Zn₂GeO₄ core–shell microspheres exhibit enhanced photocatalytic activity and stability towards photocatalytic degradation of organic pollutants.

Gold nanoparticle modified graphitic carbon nitride/multi-walled carbon nanotube (g-C3N4/CNTs/Au) hybrid photocatalysts for effective water splitting and degradation

Highly stable plasmonic potocatalysts based on Au, graphitic carbon nitride (g-C₃N₄), and carbon nanotubes (CNTs) hybrids for effective degradation of organic pollutant and photoelectrchemical (PEC) water splitting.