Cyano groups and oxygen adsorption dominated efficient hydrogen and hydrogen peroxide co-production on metal-free photocatalysts

The development of green and efficient hydrogen peroxide (H2O2) production is of great interest but remains challenging. Herein, we develop a new and simple strategy via locking the coplanarity in highly crystalline covalent triazine frameworks (CTFs) to remarkably boost direct photosynthesis of H2O2 from oxygen and water. The exfoliated ultrathin 2D-CTF nanosheets exhibit excellent photocatalytic H2O2 evolution with an ultrahigh solar-to-chemical efficiency of 0.91% and a superb apparent quantum yield of 16.8% at 420 nm, surpassing all previous CTFs and most of the metal-free photocatalysts ever reported. Our detailed experimental and theoretical studies reveal that the spatially locked structure in the crystalline CTF photocatalyst can not only greatly enhance the separation and transfer of photoexcited charge-carriers for promoting H2O2 photogeneration but also alter the local electronic structures that unexpectedly turn water oxidation from a four-electron route to a two-electron pathway, resulting in a 100% atom utilization efficiency. This work provides valuable insights into the designed synthesis of highly efficient metal-free photocatalysts and precise control over photocatalytic reaction pathways in organic materials.

Design of metal-free photocatalysts with customized chemical structure and nano-architecture is promising for photocatalytic hydrogen peroxide (H2O2) production. Herein, for the first time, mesoporous resorcinol-formaldehyde (MRF) nanobowls with optimized benzenoid-quinoid donor-acceptor (D-A) couples have been synthesized via an assembly-hydrothermal-etching process as high-performance photocatalysts for H2O2 production in a sacrificial agent-free system. At the hydrothermal temperature of ∼ 250 °C, MRF-250 exhibits optimized structural features including a large surface area, suitable D-A couple ratio, enhanced light absorption, charge-hole separation and mass transfer. Thus, MRF-250 shows an unexpected H2O2 yield of 19.4 mM·g−1·h−1 in pure water, outperforming other RF samples prepared under different conditions and superior to most reported metal-free photocatalysts without the aid of sacrificial agents. Our work paves the way towards the elaborate design of highly effective metal-free photocatalysts for H2O2 production.

The metal-free photocatalyst CN1.8/ICT/CDs by photo-charge regulation of CDs exhibits an excellent and stable H2O2 yield under visible light in air atmosphere without sacrificial agent (2202.81 μmol h−1 g−1).

A step-by-step design for dual channel metal-free photocatalysts towards high yield H2O2 photo-production from air and water

Coproduction of hydrogen (H2) and hydrogen peroxide (H2O2) from water splitting is one of the most promising ways to alleviate the energy crisis and environmental pollution. Here, we first show the synthesis and photocatalytic property of an organic semiconductor (DAnTMS compound) from 9,10-dibromoanthracene and trimethylsilylacetylene. Then, a metal-free photocatalyst of a DAnTMS/carbon dot (DAnTMS/CD) composite was designed and fabricated, which achieved the efficient photocatalytic production of H2 and H2O2 without usage of any organic solvents and sacrificial agents. Under visible light, the DAnTMS/CD composite could produce H2O2 with a maximum rate of 396.7 μmol g-1 h-1 and H2 with a maximum rate of 265.0 μmol g-1 h-1 in pure water. Transient photovoltage tests showed that CDs changed the interfacial electron transfer kinetics and served as the active site for highly efficient H2 evolution. This work provided a deep insight into the function of CDs in regulating the catalytic property of organic photocatalysts.

Introducing Br, K, and cyano group into carbon nitride for efficient photocatalytic hydrogen peroxide production then in situ tetracycline mineralization

Highly efficient unitized regenerative hydrogen peroxide cycle cell with ultralow overpotential for renewable energy storage

Metal-organic framework-derived manganese ferrite nanocubes for efficient hydrogen peroxide sensing

Enhanced O2 adsorption and favorable oxygen-intermediate desorption are essential for efficient electrochemical hydrogen peroxide production (EHPP) via the two-electron oxygen reduction reaction (2e- ORR). Here, we report an amorphous/crystalline Ni-NiO electrocatalyst synthesized via a partial reduction strategy. By engineering the amorphous/crystalline interfacial strain through varying the reduction time, the optimized Ni/NiO catalyst achieves a hydrogen peroxide selectivity of 91.78% with a Faradaic efficiency of 97.47%. It maintains a high H2O2 yield of 949.5 mM/g-1cat h-1 across three electrode systems, outperforming most Ni-based benchmarks. Density functional theory calculations and in situ characterizations reveal that strain at unsaturated Ni sites promotes electron redistribution and Ni-O bond lengthening, thereby shifting the d-p band center difference to favor O2 adsorption while weakening *OOH binding. The enhanced O2 adsorption and accelerated *OOH desorption direct the ORR pathway toward the two-electron route for H2O2 generation. Furthermore, the in situ generated H2O2 effectively degrades organic pollutants, indicating its practical utility in water remediation. This work presents the strain engineering approach in amorphous/crystalline Ni/NiO heterostructures for high-performance EHPP and selective two-electron ORR.

Covalent organic frameworks (COFs) are often employed in oxygen reduction reactions (ORR) for hydrogen peroxide production due to their tunable structures and compositions. However, COF electrocatalysts require precise structural engineering, such as heteroatoms or metal site doping, to modulate the reaction pathway during the ORR process. In this work, we designed a tetraphenyl-p-phenylenediamine based COF electrocatalyst, namely TPDA-BDA, which exhibited excellent two-electron (2e) ORR performance with high H2O2 selectivity of 89.7 % and faraday efficiency (FE) of 86.7 %, higher than the reported COFs to date for H2O2 electrosynthesis. The theoretical and experimental results showed that the rate-determining step energy barrier for reduction of O2 to OOH* intermediates was significantly reduced by replacing of bipyridine with biphenyl blocks, changing from 4e to 2e ORR reaction pathway. Also, the donor-acceptor characteristic and narrower optical band gap of TPDA-BDA COF enhanced the electronic conductivity and reduction ability, thus elevating the catalytic activity. As a result, the H2O2 selectivity was maintained above 85 % even after 50 h stability test. This work reveals the structure-property relationship of COF electrocatalysts and provides a new strategy for rational design of high performance 2e ORR COF electrocatalysts for efficient and selective hydrogen peroxide production.

Hydrogen peroxide (HP) is a promising chemical sanitizer for use in the food industry. Its residues have to be decomposed, usually using an enzyme process employing catalase. In order to offer an inexpensive biocatalyst and to simplify subsequent manipulation, we have prepared magnetically responsive alginate beads containing entrapped Saccharomyces cerevisiae cells and magnetite microparticles. Larger beads (2-3 mm in diameter) were prepared by dropping the mixture into calcium chloride solution, while microbeads (the diameter of majority of particles ranged between 50 and 100 microm) were prepared using the water in oil emulsification process. In general, microbeads enabled more efficient HP decomposition. The prepared microparticulate biocatalyst caused efficient decomposition of HP in water solutions (up to 2% concentration), leaving very low residual HP concentration after treatment (below 0.001% under appropriate conditions). The biocatalyst was stable; the same catalytic activity was observed after one month storage at 4 degrees C, and the microbeads could be used at least five times.

The photocatalytic transformation of CO2 to valuable man-made feedstocks is a promising method for balancing the carbon cycle; however, it is often hampered by the consumption of extra hole scavengers. Here, a synergistic redox system using photogenerated electron-hole pairs was constructed by employing a porous carbon nitride with many cyanide groups as a metal-free photocatalyst. Selective CO2 reduction to CO using photogenerated electrons was achieved under mild conditions; simultaneously, various alcohols were effectively oxidized to value-added aldehydes using holes. The results showed that thermal calcination process using ammonium sulfate as porogen contributes to the construction of a porous structure. As-obtained cyanide groups can facilitate charge carrier separation and promote moderate CO2 adsorption. Electron-donating groups in alcohols could enhance the activity via a faster hydrogen-donating process. This concerted photocatalytic system that synergistically utilizes electron-hole pairs upon light excitation contributes to the construction of cost-effective and multifunctional photocatalytic systems for selective CO2 reduction and artificial photosynthesis.

Recently, various metal peroxide nanomaterials have drawn increasing attention as an efficient hydrogen peroxide (H2O2) self-supplying agent for enhanced tumor therapy. However, a single kind of metal peroxide is insufficient to achieve more effective antitumor performance. Here, a hyaluronic acid modified calcium and copper peroxides nanocomposite has been synthesized by a simple one-step strategy. After effective accumulation at the tumor site due to the enhanced permeability and retention (EPR) effect and specific recognition of hyaluronate acid with CD44 protein on the surface of tumor cells, plenty of Ca2+, Cu2+, and H2O2 can be simultaneously released in acid and hyaluronidase overexpressed tumor microenvironment (TME), generating abundant hydroxyl radical through enhanced Fenton-type reaction between Cu2+ and self-supplying H2O2 with the assistance of glutathione depletion. Overloaded Ca2+ can lead to mitochondria injury and thus enhance the oxidative stress in tumor cells. Moreover, an unbalanced calcium transport channel caused by oxidative stress can further promote tumor calcification and necrosis, which is generally defined as ion-interference therapy. As a result, the synergistic effect of Fenton-like reaction by Cu2+ and mitochondria dysfunction by Ca2+ in ROS generation is performed. Therefore, a TME-responsive calcium and copper peroxides nanocomposite based on one-step integration has been successfully established and exhibits a more satisfactory antitumor efficiency than any single kind of metal peroxide.

Metal peroxide nanomaterials as efficient hydrogen peroxide (H2O2) self-supplying agents have attracted the attention of researchers for antitumor treatment. However, relying solely on metal peroxides to provide H2O2 is undoubtedly insufficient to achieve optimal antitumor effects. Herein, we construct novel hyaluronic acid (HA)-modified nanocomposites (MgO2/Pd@HA NCs) formed by decorating palladium nanoparticles (Pd NPs) onto the surfaces of a magnesium peroxide (MgO2) nanoflower as a highly effective nanoplatform for the tumor microenvironment (TME)-responsive induction of ferroptosis in tumor cells and tumor photothermal therapy (PTT). MgO2/Pd@HA NC could be well endocytosed into tumor cells with CD44 expression depending on the specific recognition of HA with CD44, and then, the nanocomposites can be rapidly decomposed in mild acid and hyaluronidase overexpressed TME, and plenty of H2O2 was released. Simultaneously, Pd NPs catalyze self-supplied H2O2 to generate abundant hydroxyl radicals (•OH) and catalyze glutathione (GSH) into glutathione disulfide owing to its peroxidase and glutathione oxidase mimic enzyme activities, while the abundant •OH could also consume GSH in tumor cells and disturb the defense pathways of ferroptosis leading to the accumulation of lipid peroxidation and resulting in the occurrence of ferroptosis. Additionally, the superior photothermal conversion performance of Pd NPs in near-infrared II could also be used for PTT, synergistically cooperating with nanocomposite-induced ferroptosis for tumor inhibition. Consequently, the successfully prepared TME-responsive MgO2/Pd@HA NCs exhibited marked antitumor effect without obvious biotoxicity, contributing to thoroughly explore the nanocomposites as a novel and promising treatment for tumor therapy.

Split dosing of H2O2 for enhancing recalcitrant organics removal from landfill leachate in the Fe0/H2O2 process: Degradation efficiency and mechanism