Graphite-N reinforced sludge biochar electrode: A experimental and DFT theoretical analysis of efficient evolution and in-situ utilization of H2O2.

Rational reuse of municipal sludge to produce electro-Fenton electrode can not only save resources, but also produce superior peroxide and degradation pollutants simultaneously. Herein, a novel electro-Fenton electrode derived from sludge biochar loaded on Ni foam (SBC@Ni) was constructed via high temperature pyrolysis and chemical coating for efficient H2O2 evolution and pollutant degradation. Systematic experiments and density functional theory calculations (DFT calculation) explained that the production of graphite C and graphite N during high-temperature pyrolysis of municipal sludge can greatly enhance the oxygen reduction reaction of SBC@Ni electrode and promote the evolution of H2O2. And the hybrid heterojunctions, such as FeP, also played a key role in electrocatalytic processes. Notably, the electrode still exhibited excellent performance after 1000 linear scans and 12 h of continuous current stimulation, which demonstrated the excellent stability of the electrode. Moreover, SBC@Ni electrode can not only effectively oxidize 4-chlorophenol through the electro-Fenton effect, but also fully mineralize organic matter, indicating promising environmental application. The free radical quenching experiment also revealed that the ·OH is the main active species for 4-CP degradation in SBC@Ni electro-Fenton system.

Few-Layer Meets Crystalline Structure: Collaborative Efforts for Improving Photocatalytic H2O2 Generation over Carbon Nitride.

Although the conversion of O2 and H2O to H2O2 over graphite carbon nitride (g-C3N4) has been realized by means of the photocatalytic process, the catalytic activity of pristine g-C3N4 is still restricted by the rapid charge recombination and inadequate exposure of the active site. In this work, we propose a straightforward strategy to solve these limitations by decreasing the thickness and improving the crystallinity of g-C3N4, resulting in the preparation of few-layered crystalline carbon nitride (FL-CCN). Benefiting from the minimal thickness and highly ordered in-plane triangular cavities within the structure, FL-CCN processes an extended π-conjugated system with a reduced charge transfer resistance and expanded specific surface area. These features accelerate the efficiency of photogenerated charge separation in FL-CCN and contribute to explore of its surface active sites. Consequently, FL-CCN exhibits a significantly improved H2O2 evolution rate (63.95 µmol g-1 h-1), which is 7.8 times higher than that of pristine g-C3N4 (8.15 µmol g-1 h-1), during the photocatalytic conversion of O2 and H2O. This systematic investigation offers valuable insights into the mechanism of photocatalytic H2O2 generation and the development of efficient catalysts.

G-C3N4 sheet nanoarchitectonics with island-like crystalline/amorphous homojunctions towards efficient H2 and H2O2 evolution.

Photocatalystic evolution of H2O2 from water and oxygen has attracted significant attention because of environmentally friendly. The absorption in visible and hydrophilic feature of graphitic carbon nitride (g-C3N4) make it a good candidate. In this paper, a rapid post-treatment at high temperature was developed to obtain g-C3N4 nanosheets with abundant crystalline/amorphous interfaces to form homojunctions, which optimized uniplanar carrier mobility dynamics. The conversion from bulk to two-dimensional g-C3N4 resulted from the breakage of interplanar hydrogen bonds and interlayer Van der Waals force. The unique morphology not only rendered photocatalyst with larger specific surface area but also inhibited the robust volume recombination of charge carriers. The accelerated charge carriers flow at the interface, interplane and interlayer together ameliorated the separation and transfer of electrons and holes. A new-emerged n→π* transition ameliorated the poor light utilization efficiency. Beyond the increased photocatalytic H2 evolution property (779.2 µmol g-1 h-1), optimized sample displayed a H2O2 evolution activity as high as 4877.1 µM g-1 h-1 under visible light illumination, which was ∼5.8 times of that of bulk g-C3N4. Detailed photocatalytic mechanism investigation manifested that the two-step single-electron oxygen reduction process occupied the dominant status in H2O2 evolution. This work proposed a novel strategy for obtaining g-C3N4 homojunctions as a promising bi-functional metal-free catalyst to be applied in clean energy production field.

Oxygen-modified graphitic carbon nitride with nitrogen-defect for metal-free visible light photocatalytic H2O2 evolution.

Photocatalytic oxygen reduction is regarded as the cleanest approach for the production of hydrogen peroxide (H2O2). Herein, oxygen-modified graphite carbon nitride (g-C3N4) with nitrogen-defect (namely g-C3N4-ND4-OM3) was synthesized by a feasible method. Owing to the existence of nitrogen vacancy and oxygen-containing functional group, the absorption bands derived from n â†’ π* and π â†’ π* electronic transitions were enhanced, thereby enlarging the visible light response range of catalysts. Interestingly, nitrogen-defect can capture electron and effectively suppress the recombination of photoinduced electrons and holes. More importantly, the introduction of oxygen-containing functional groups can improve the hydrophilicity of g-C3N4, which was beneficial for the adsorption of dissolved oxygen. The electrostatic potential distributions of g-C3N4-based photocatalyst structural unit were also changed after introducing nitrogen vacancy and oxygen-containing functional group, and the electron-donating ability of g-C3N4 was improved. As a result, the evolution rate of H2O2 catalyzed by g-C3N4-ND4-OM3 was as high as 146.96 µmol/g/L under visible light irradiation. The photocatalytic H2O2 generation was completed through the direct 2-e- oxygen reduction. In short, current work will share novel insights into photocatalytic H2O2 generation over g-C3N4-based catalyst.

Covalent Organic Frameworks for Energy Conversion in Photocatalysis.

Intensifying energy crises and severe environmental issues have led to the discovery of renewable energy sources, sustainable energy conversion, and storage technologies. Photocatalysis is a green technology that converts eco-friendly solar energy into high-energy chemicals. Covalent organic frameworks (COFs) are porous materials constructed by covalent bonds that show promising potential for converting solar energy into chemicals owing to their pre-designable structures, high crystallinity, and porosity. Herein, we highlight recent progress in the synthesis of COF-based photocatalysts and their applications in water splitting, CO2 reduction, and H2 O2 production. The challenges and future opportunities for the rational design of COFs for advanced photocatalysts are discussed. This Review is expected to promote further development of COFs toward photocatalysis.

Rational modification of hydroxy-functionalized covalent organic frameworks for enhanced photocatalytic hydrogen peroxide evolution.

Covalent organic frameworks (COFs), a class of flexibly tunable crystalline materials, have fascinating potential in photocatalytic hydrogen peroxide (H2O2) evolution under visible light irradiation. However, achieving efficient catalytic activity by tuning the composition of COFs and the linkages of building blocks is still a challenge. Herein, four imine-linked COFs with different numbers of hydroxy-functionalized are constructed to unveil the latent structure-activity relationship between the reversibility of bonding in supramolecular chemistry and the photocatalytic H2O2 performance. As the optimized material, TAPT-HTA-COF (1H-COF) containing single hydroxy group in aldehyde node exhibits a highest ordered structure and conjugation degree along and across the plane in the extended frameworks originating from the flexibly reversible iminol-to-ketoenamine tautomerism than others, which broadens the visible light absorption and accelerates the dissociation of photogenerated carriers in 1H-COF. These merits ensure that 1H-COF has the highest H2O2 yield (44.5 µmol L-1) and O2 two-electron reduction pathway among the four COFs under visible light irradiation (λ > 420 nm, 10 vol% isopropanol aqueous solution). At the same time, the long-range ordered framework of 1H-COF is well preserved during the photocatalytic H2O2 evolution process assisted by the proton-induced tautomerization. This work facilitates the design and development of COF-based photocatalysts in the evolution of H2O2.

Suppressing Water Dissociation via Control of Intrinsic Oxygen Defects for Awakening Solar H2 O-to-H2 O2 Generation.

BiVO4 theoretically has a thermodynamic activity trend toward highly selective water oxidative H2 O2 formation, but it is more inclined to generate O2 in practical. The influence of intrinsic oxygen vacancy (Ovac ), especially, on surface reactivity, has never been considered as a possible activity loss mechanism in the synthetic BiVO4 . In this work, it is theoretically and experimentally demonstrated that the intrinsic surface Ovac is responsible for lower H2 O2 evolution activity via promoting water dissociation to form intermediate. Through an annealing process under a V2 O5 rich atmosphere, the surface Ovac can be eliminated that awakens the photoelectrochemical (PEC) water oxidative H2 O2 activity in a NaHCO3 electrolyte, which achieves an average of 58.4%, and increases by up to 4.28 times of the one annealed in air. This work offers a general understanding of catalytic activity loss and may be extended to other photo or electrocatalysts for catalytic selectivity regulation.