Microwave-assisted synthesis of nanocrystalline binary and ternary metal oxides

Interplay of chemistry and nanotechnology has effectively substantiated the ever-expanding horizons of materials chemistry, leading to a paradigm shift in (nano)materials synthesis. Current challenges of chemically processed materials include efforts to redesign synthetic procedures by using less hazardous starting materials, choosing milder reaction conditions, shortening time scale of chemical transformations and most importantly reduction of energy requirements. In this context, successful substitution of classical energy input by microwave radiation is a promising alternative in most fields of common chemical synthesis. This review highlights the latest developments in the synthesis of advanced inorganic materials by microwave-assisted chemical reactions. When compared to conventional convective and conductive heating techniques, microwave irradiation provides efficient internal volumetric heating through generation of localised high temperature zones in the reaction media by direct coupling of microwave energy to the molecules present in the reaction mixture, thereby enabling rapid synthesis with superior yield and both reduced reaction time as well as processing steps. Abbreviations: [BMIM]BF4: 1-butyl-3-methylimidazolium tetrafluoroborate; [C2mim][NTf2]: 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide; [C4mim][NTf2]: 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide; [C12Py][ClO4]: N-dodecylpyridinium perchlorate; [OMIM]TA: 1-octyl-3-methylimidazolium trifluoroacetate; AAO: anodic aluminium oxide; acac: acetylacetone; CNCs: colloidal nanocrystal clusters; CTAB: cetrimonium bromide; DEG: diethylene glycol; EDA: ethylenediamine; EG: ethylene glycol; EGMM: 2-methoxyethanol; FESEM: field emission scanning electron microscopy; FTO: fluorine-doped tin oxide; h: hours; HMT: hexamethylenetetramine; HR-TEM: high-resolution transmission electron microscopy; HPC: hydroxypropyl cellulose; IL: ionic liquids; ITO: indium tin oxide; MEA: ethanolamine; min: minutes; MPA: 3-mercaptopropionic acid; MW: microwave; nm: nanometre; NMP: n-methyl-2-pyrrolidon; OP: p-octyl polyethylene glycol phenylether; P(VP-NVP-St): polyvinylpyrrolidone-polyvinylpyrrolidone-polystyrene; P-103: polyethyleneoxide–polypropyleneoxide–polyethyleneoxide copolymer; PAA: polyacrylic acid; PC: polycarbonate; PEG: polyethylene glycol; PEG-PPO-PEG: poly(ethylene glycol-poly(p-phenyleneoxide)-poly(ethylene glycol); PET: polyethylene terephthalate; Pluronic P123: triblock copolymer; poly(ethyleneglycol)-block-poly(propyleneglycol)-block-poly(ethylene glycol); Pluronic F127: poloxamer; PPO: poly(p-phenyleneoxide); PS(540)-b-PEO(220): polystyrene-block-poly(ethyleneoxide) diblock copolymer with 540 monomerunits of styrene and 220 monomer units of ethylene oxide; PVA: polyvinyl alcohol; PVP: polyvinylpyrrolidone; QDs: quantum dots; R: ratio; s: seconds; SBA-15: Santa Barbara Amorphous-15 (mesostructured silica); SDBS: sodium dodecylbenzenesulfonate; SDS: sodium dodecyl sulphate; tan δ: dielectric loss factor; TBAH: tetrabutylammonium hydroxide; TEAB: tetraethylammonium bromide; TEG: triethylene glycol; TEM: transmission electron microscopy; TMAH: tetramethylammonium hydroxide; TMP: 2,2,6,6-tetramethylpiperidine; TOPO: trioctyl phosphine oxide; TTIP: titanium isopropoxide