No abstract

Currently, precious metal group materials are known as the efficient and widely used oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalysts. The exorbitant prices and scarcity of the precious metals have stimulated scale exploration of alternative non-precious metal catalysts with low-cost and high performance. Layered double hydroxides (LDHs) are a promising precursor to prepare cost-effective and high-performance catalysts because they possess abundant micropores and nitrogen self-doping after pyrolysis, which can accelerate the electron transfer and serve as active sites for efficient OER. Herein, we developed a new highly active NiFeMn-layered double hydroxide (NFM LDH) based electrocatalyst for OER. Through building NFM hydroxide/oxyhydroxide heterojunction and incorporation of conductive graphene, the prepared NFM LDH-based electrocatalyst delivers a low overpotential of 338 mV at current density of 10 mA cm−2 with a small Tafel slope of 67 mV dec−1, which are superior to those of commercial RuO2 catalyst for OER. The LDH/OOH heterojunction involves strong interfacial coupling, which modulates the local electronic environment and boosts the kinetics of charge transfer. In addition, the high valence Fe3+ and Mn3+ species formed after NaOH treatment provide more active sites and promote the Ni2+ to higher oxidation states during the O2 evolution. Moreover, graphene contributes a lot to the reduction of charge transfer resistance. The combining effects have greatly enhanced the catalytic ability for OER, demonstrating that the synthesized NFM LDH/OOH heterojunction with graphene linkage can be practically applied as a high-performance electrocatalyst for oxygen production via water splitting.

Photocatalytic technology is currently the most promising technology for environmental pollution control. The preparation of photocatalysts with excellent properties is the core of the development of photocatalytic technology. TiO2 can form a heterojunction with g-C3N4, which can effectively inhibit the recombination of photogenerated electron–hole pairs, improve the mobility of photogenerated carriers, and thus improve the photocatalytic performance. In this study, NaCl was used as a template, and the loose and porous g-C3N4/TiO2 heterojunction composite photocatalysts were prepared by the template method. Compared to the pure g-C3N4 prepared by the conventional thermal polycondensation method and TiO2, the g-C3N4/TiO2 heterojunction composite photocatalysts prepared in this study exhibited a greatly increased specific surface area, an improved light absorption performance, a significantly suppressed recombination of photogenerated electrons and holes. Furthermore, the g-C3N4/TiO2 heterojunction composite photocatalysts exhibited excellent photocatalytic performance.

Photocatalytic degradation is one of the most promising emerging technologies for environmental pollution control. However, the preparation of efficient, low-cost photocatalysts still faces many challenges. TiO2 is a widely available and inexpensive photocatalyst material, but improving its catalytic degradation performance has posed a significant challenge due to its shortcomings, such as the easy recombination of its photogenerated electron–hole pairs and its difficulty in absorbing visible light. The construction of homogeneous heterojunctions is an effective means to enhance the photocatalytic performances of photocatalysts. In this study, a TiO2(B)/TiO2(A) homogeneous heterojunction composite photocatalyst (with B and A denoting bronze and anatase phases, respectively) was successfully constructed in situ. Although the construction of homogeneous heterojunctions did not improve the light absorption performance of the material, its photocatalytic degradation performance was substantially enhanced. This was due to the suppression of the recombination of photogenerated electron–hole pairs and the enhancement of the carrier mobility. The photocatalytic ability of the TiO2(B)/TiO2(A) homogeneous heterojunction composite photocatalyst was up to three times higher than that of raw TiO2 (pure anatase TiO2).

Research has demonstrated that the formation of composites of titanium dioxide (TiO2) with silver phosphate (Ag3PO4) through the construction of heterojunctions can expand its light absorption range and suppress the recombination of photogenerated electron–hole pairs, thereby improving the photocatalytic performance. However, this method offers only limited performance improvements, and the composite photocatalysts are costly due to the expensive Ag3PO4. In this study, Ti3C2 MXene, which has good hydrophilicity and excellent electrical conductivity, is first used to form Schottky junction composites with bronze TiO2 (TiO2(B)) via electrostatic self-assembly. Then, Ag3PO4 quantum dots were further formed on the surface of the TiO2(B)/Ti3C2 MXene by in situ self-growth, and Ag3PO4 formed heterojunctions and Schottky junctions with TiO2(B) and Ti3C2 MXene, respectively. Finally, a ternary composite photocatalyst TiO2(B)/Ti3C2 MXene/Ag3PO4 was jointly constructed by these functional junctions. Under the synergistic effect of these functional junctions, the mobility and fast separation performance of photogenerated electron–hole pairs of the composite photocatalyst were significantly improved, the recombination of photogenerated electron–hole pairs was effectively suppressed, and the light absorption performance was enhanced. As a result, the composite photocatalyst exhibited excellent photocatalytic performances.