Unsupported and silica-supported nickel nanoparticles: synthesis and application in catalysis

In recent years, nickel nanoparticles (Ni NPs) have attracted a growing attention from the scientific research community, because they are inexpensive, eco-friendly, facile to prepare, and they could be used in a panoply of applications, ranging from catalysis to sensors and from fuel cells to photoelectrochemical devices. This review article recapitulates different synthesis methods which have been used to prepare unsupported and silica-supported Ni NPs and their utilisation as nanocatalysts in heterogeneous catalysis and photocatalysis. Firstly, various widely used techniques to synthesize unsupported Ni NPs have been briefly discussed. This includes ball milling, mechanochemical synthesis, laser ablation, and ion sputtering as top–down methods, and physical vapour deposition, chemical vapour deposition, sol–gel method, chemical precipitation, chemical reduction, hydrothermal method, solvothermal, spray pyrolysis, and biological techniques as bottom–up methods. Subsequently, the widely applied methods to incorporate Ni NPs in different types of silica (e.g. SBA-15, MCM-41, MCM-48, TUD-1) are briefly reviewed including impregnation, precipitation, and colloid methods. Finally, recent applications of both unsupported and supported Ni NPs in heterogeneous catalysis and photocatalysis have been discussed, with brief investigation of the effect of Ni NP size and aggregation on their catalytic activity and reusability.