Molybdenum impregnated g-C3N4 nanotubes as potentially active photocatalyst for renewable energy applications

Inorganic-Organic Dual-Ligand-Regulated Photocatalysis of CdS@ZnxCd1-xS@ZnS Quantum Dots for Lignin Valorization

In a dual-functional lignin valorization system, a harmonious oxidation and reduction rate is a prerequisite for high photocatalytic performance. Herein, an efficient and facile ligand manipulating strategy to balance the redox reaction process is exploited via decorating the surface of the CdS@ZnxCd1-xS@ZnS gradient-alloyed quantum dots with both inorganic ligands of hexafluorophosphate (PF6-) and organic ligands of mercaptopropionic acid (MPA). Inorganic ion ligands in this system provide a promotion for intermediator reduction reactions. By optimizing the ligand composition on the quantum dot surface, we achieve precise control over the extent of oxidation and reduction, enabling selective modification of reaction products; that is, the conversion rate of 2-phenoxy-1-phenylethanol reached 99%. Surface engineering by regulating the ligand type demonstrates that PF6- and thiocyanate (SCN-) inorganic ion ligands contribute significantly toward electron transfer, while MPA ligands have beneficial effects on the hole-transfer procedure, which is predominantly dependent on their steric hindrance, electrostatic action, and passivation effect. The present study offers insights into the development of efficient quantum dot photocatalysts for dual-functional biomass valorization through ligand design.

Enriched photocatalytic and photoelectrochemical activities of a 2D/0D g-C3N4/CeO2 nanostructure

Sunlight-powered photocatalysts made from CeO2 nanosized particles and g-C3N4 nanostructures were produced through a thermal decomposition process with urea and cerium nitrate hexahydrate. The preparation of g-C3N4, CeO2, and a binary nanostructured g-C3N4/CeO2 photocatalyst was done through a facile thermal decomposition method. The structural properties were analyzed using powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy (XPS). Photocatalyst properties were characterized by using crystal violet (CV), a UV-Vis spectrophotometer, photocurrent and electron impedance spectroscopy (EIS). The structural and morphological analyses revealed that the g-C3N4/CeO2 nanostructures significantly enhanced the photoactivity for CV dye degradation under simulated sunlight, with a degradation rate of 94.5% after 105 min, compared to 82.5% for pure g-C3N4 and 45% for pure CeO2. This improvement was attributed to the noticeable visible light absorption and remarkable charge separation abilities of the nanostructures. Additionally, the g-C3N4/CeO2 nanostructures showed notable PEC performance under simulated sunlight. This study presents an easy and efficient method for producing g-C3N4 photocatalysts decorated with semiconductor materials and provides insights for designing nanostructures for photocatalytic and energy applications.

Functionalized 2D defect g-C3N4 for artificial photosynthesis of H2O2 and synchronizing tetracycline fluorescence detection and degradation

Artificial photosynthesis of H₂O₂ is a clean production technology, which brings the synergistic effect to photodegradation of pollutants. Inspired by defect engineering, 2D defective carbon nitride (g-C₃N₄) photocatalyst was obtained via potassium ion assisted synthesis. Defective g-C₃N₄ is protonated and applied to photosynthesis of H₂O₂, H₂O₂ concentration produced reached 477.7 μM, which was approximately 5.27 times that by pristine g-C₃N₄. Additionally, defective g-C₃N₄ materials are borrowed to synchronizing tetracycline (TC) fluorescence detection and degradation, suggesting the catalyst existed bifunctional characteristics of TC detection and degradation. Meanwhile, metal impregnation engineering (molybdenum) was borrowed enhancing the electron-trapping ability in local region of defective g-C₃N₄, which takes advantages to the efficient degradation of TC. Furthermore, optical and electrical properties of photocatalysts were investigated in details by advanced material characterization testing. This work provides potential applications in the field of artificial photosynthesis and pollution degradation.

Advanced Photoelectrochemical Hydrogen Generation by CdO-g-C3N4 in Aqueous Medium under Visible Light

Herein, hydrothermal fabrication of CdO-g-C₃N₄ photocatalyst for a substantially better photocatalytic recital in water splitting is presented. The XRD analysis confirms the cubic phase of CdO-g-C₃N₄, whereas FTIR and UV-VIS studies revealed the presence of respective groups and a median band gap energy (2.55 eV) of the photocatalyst, respectively, which further enhanced its photo-electrochemical (PEC) properties. The SEM displays the oblong structures of g-C₃N₄ sheets and nano rod-like morphology of CdO and CdO-g-C₃N₄, respectively. The HR-TEM exhibits morphology & orientation of the grains and substantiates the polycrystal-line nature of CdO-g-C₃N₄ nanocomposite. The photocatalytic water-splitting concert is evaluated by PEC experiments under 1 SUN visible light irradiation. Linear sweep voltammetry (LSV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) comprehend the CdO-g-C₃N₄ as a hydrogen evolution photocatalyst. A photocurrent density beyond ≥5 mA/cm² is recorded from CdO-g-C₃N₄, which is 5-6 folds greater than pure CdO and g-C₃N₄. The efficient separation and transfer of charges allocated to CdO-g-C₃N₄ and fabricating heterojunctions between g-C₃N₄ and CdO suppresses the unfavorable electron-hole pairs recombination process. Thus, it recesses charge transfer resistance, augmenting enhanced photocatalytic performance under 1 SUN irradiation.

A Comprehensive Review on Graphitic Carbon Nitride for Carbon Dioxide Photoreduction

Inspired by natural photosynthesis, harnessing the wide range of natural solar energy and utilizing appropriate semiconductor-based catalysts to convert carbon dioxide into beneficial energy species, for example, CO, CH₄ , HCOOH, and CH₃ COH have been shown to be a sustainable and more environmentally friendly approach. Graphitic carbon nitride (g-C₃ N₄ ) has been regarded as a highly effective photocatalyst for the CO₂ reduction reaction, owing to its cost-effectiveness, high thermal and chemical stability, visible light absorption capability, and low toxicity. However, weaker electrical conductivity, fast recombination rate, smaller visible light absorption window, and reduced surface area make this catalytic material unsuitable for commercial photocatalytic applications. Therefore, certain procedures, including elemental doping, structural modulation, functional group adjustment of g-C₃ N₄ , the addition of metal complex motif, and others, may be used to improve its photocatalytic activity towards effective CO₂ reduction. This review has investigated the scientific community's perspectives on synthetic pathways and material optimization approaches used to increase the selectivity and efficiency of the g-C₃ N₄ -based hybrid structures, as well as their benefits and drawbacks on photocatalytic CO₂ reduction. Finally, the review concludes a comparative discussion and presents a promising picture of the future scope of the improvements.

Light Promotes the Immobilization of U(VI) by Ferrihydrite

The environmental behaviors of uranium closely depend on its interaction with natural minerals. Ferrihydrite widely distributed in nature is considered as one main natural media that is able to change the geochemical behaviors of various elements. However, the semiconductor properties of ferrihydrite and its impacts on the environmental fate of elements are sometimes ignored. The present study systematically clarified the photocatalysis of U(VI) on ferrihydrite under anaerobic and aerobic conditions, respectively. Ferrihydrite showed excellent photoelectric response. Under anaerobic conditions, U(VI) was converted to U(IV) by light-irradiated ferrihydrite, in the form of UO2+x (x < 0.25), where •O2− was the dominant reactive reductive species. At pH 5.0, ~50% of U(VI) was removed after light irradiation for 2 h, while 100% U(VI) was eliminated at pH 6.0. The presence of methanol accelerated the reduction of U(VI). Under aerobic conditions, the light illumination on ferrihydrite also led to an obvious but slower removal of U(VI). The removal of U(VI) increased from ~25% to 70% as the pH increased from 5.0 to 6.0. The generation of H2O2 under aerobic conditions led to the formation of UO4•xH2O precipitates on ferrihydrite. Therefore, it is proved that light irradiation on ferrihydrite significantly changed the species of U(VI) and promoted the removal of uranium both under anaerobic and aerobic conditions.

Synthesis of a UiO-66/g-C3N4 composite using terephthalic acid obtained from waste plastic for the photocatalytic degradation of the chemical warfare agent simulant, methyl paraoxon

In our study, Zr-based UiO-66 (Zr) was synthesized using terephthalic acid obtained from waste plastic. Thereafter, UiO-66/g-C₃N₄ composites were prepared by the solvothermal method, and their photocatalytic activity in the photodegradation of the chemical warfare agent simulant, dimethyl 4-nitrophenyl phosphate (DMNP), was evaluated. The as-synthesized UiO-66/g-C₃N₄ exhibited a high surface area (1440 m² g⁻¹) and a high capillary volume (1.49 cm³ g⁻¹). The UiO-66/g-C₃N₄ samples absorbed a visible light band with bandgap energies of 2.13–2.88 eV. The as-synthesized UiO-66/g-C₃N₄ composites exhibited highly efficient degradation of DMNP with a short half-life (t_1/2 of 2.17 min) at pH 7 under visible light irradiation. The trapping experiments confirmed that the h⁺ and ˙O₂⁻ radicals played an important role in the photocatalytic degradation of DMNP. The UiO-66/g-C₃N₄ catalyst simultaneously performed two processes: the hydrolysis and photocatalytic oxidation of DMNP in water. During irradiation, a p–n heterojunction between UiO-66 and g-C₃N₄ restricted the recombination of photogenerated electrons and holes, resulting in the enhancement in the degradation rate of DMNP.

UiO-66/g-C₃N₄ with a high surface area (1440 m² g⁻¹) and a high capillary volume (1.49 cm³ g⁻¹) exhibited highly efficient degradation of dimethyl 4-nitrophenyl phosphate with t_1/2 = 2.17 min.

Tailoring g-C3N4 with Lanthanum and Cobalt Oxides for Enhanced Photoelectrochemical and Photocatalytic Activity

Herein, the synthesis, characterization, and photoelectrochemical and photocatalytic characteristics of hydrothermally prepared La2O3–g-C3N4, CoO–g-C3N4, and La2O3–CoO–g-C3N4 are discussed. The XRD analysis and crystalline phases unveiled the impregnation of La2O3 and CoO into g-C3N4. The microscopic analysis supports the formation of g-C3N4 nanoflakes and La2O3 and CoO nanoparticles embedded homogeneously in the La2O3–CoO–g-C3N4 nanocomposite, whereas the EDX comprehended their respective elemental composition and ratios. A bandgap energy of 2.38 eV for La2O3–CoO–g-C3N4 was calculated using the Tauc plot method, complementing high visible-light activity. The solar-driven water-splitting reaction exhibited significant photocurrent efficiency (~3.75 mA/cm2), augmenting the hydrogen generation by La2O3–CoO–g-C3N4 compared to that by pure g-C3N4, La2O3–g-C3N4, and CoO–g-C3N4 in 0.5 M Na2SO4 electrolyte. The synergistic effect of La2O3 and CoO impregnation with g-C3N4 led to effective division of the photogenerated charge transporters, enhancing the photocatalytic hydrogen generation by the photocatalysts. Furthermore, photocatalytic pollutant removal, namely greater than 90% decomposition of methylene blue (MB) from water, was investigated with a pseudo-first-order reaction kinetics under 1 sun visible-light irradiation. Thus, La2O3–CoO–g-C3N4 nanocomposite was found to be a prospective material for harnessing solar energy.

Recent Trends in Graphitic Carbon Nitride-Based Binary and Ternary Heterostructured Electrodes for Photoelectrochemical Water Splitting

The graphitic carbon nitride (g-C3N4) is a class of two-dimensional layered material. The ever-growing research on this fascinating material is due to its unique visible light absorption, surface, electrocatalytic, and other physicochemical properties that can be useful to different energy conversion and storage applications. Photoelectrochemical (PEC) water splitting reaction is one of the promising applications of g-C3N4, wherein it acts as a durable catalyst support material. Very recently, the construction of g-C3N4-based binary and ternary heterostructures exhibited superior PEC water splitting performance owing to its reduced reunion of e-/h+ pairs and the fast transfer of charge carriers at the heterostructure interface. This review compiles the recent advances and challenges on g-C3N4-based heterostructured photocatalysts for the PEC water splitting reaction. After an overview of the available literature, we presume that g-C3N4-based photocatalysts showed enhanced PEC water splitting performance. Therefore, it is believed that these materials have tremendous opportunities to act as durable catalyst support for energy-related applications. However, researchers also considered several limitations and challenges for using C3N4 as an efficient catalyst support material that must be addressed. This review article provides an overview of the fundamental principles of PEC water splitting, the current PEC water splitting research trends on g-C3N4-based binary and ternary heterostructured electrodes with respect to different electrolytes, and the other key factors influencing their photoelectrochemical performance. Finally, the future research direction with several recommendations to improve the photocatalytic efficiency of these materials is also provided at the end.