Progress, Challenge, and Perspective of Bimetallic TiO₂-Based Photocatalysts

Table 3

Recent publications of preparation of bimetallic photocatalysts and their application in reduction and oxidation processes.

Bimetallic NPs	Preparation procedure	Average particle size [nm]	Pollutant	Reference
Ag-Au	Deposition-precipitation method	3 to 4	The catalysts were examined in reaction of CO oxidation. Au-Ag/TiO2 catalysts activated in H2 at high temperature (550°C) exhibit higher activity than monometallic gold catalysts containing particles of the same size. Monometallic silver catalyst was inactive	[79]
Ag-Au	Sol-gel	Metals n.m. TiO2 crystallite size 7 to 9	The photocatalytic activity was determined in the reaction of degradation of 4-chlorophenol. The presence of the 0.05% and 0.1% Au/TiO2 rapidly degraded hydroquinone (HQ) to hydroxyhydroquinone (HHQ) (i.e., intermediates from 4-chlorophenol degradation)	[80]
Ag-Au	Photodeposition	Bimodal size distribution 1 to 2 (silver NPs) and 20 (Ag-Au)	The photocatalytic activity was examined during methanol dehydrogenation (50% MeOH, argon) under UV irradiation (Hg lamp) and 2-propanol oxidation (5 vol%) under visible light irradiation (Xe lamp, 𝜆>450 nm)	[55]
Ag-Au	Microemulsion	5 to 10	The photocatalytic activity of noble metals modified TiO2 powders under visible light irradiation was estimated by measuring the decomposition rate of phenol in an aqueous solution. Bimetallic alloy samples (AgAu/TiO2) showed a higher photodegradation rate in visible region than monometallic photocatalysts	[11]
Ag-Au	Precipitation-decomposition method	4 to 100	It was found that Ag-Au-ZnO is more efficient than Ag-ZnO, Au-ZnO, bare ZnO, commercial ZnO, TiO2-P25,and TiO2 (Aldrich) for degradation of MB under UV-A light	[81]
Pt-Ir	Coimpregnation method by chemical vapor deposition. The reduction of both metallic salts was carried out under inert atmosphere at 400°C	0.9	The addition of iridium to platinum catalysts could affect directly the dispersion and size of metal particle because of synergetic and electronic effects and consequently cause an improvement in the catalytic development	[82]
Pt-Ir	Impregnation/precipitation method	1 to 2	The activity was studied in the reaction of cyclohexane dehydrogenation and cyclopentane hydrogenolysis. For both bimetallic catalyst series decalin conversion increases as Ir loading and temperature level increase	[83]
Cu-Ni	Precipitation method	11 to 35	The decolorization of Orange II was studied under visible light using bimetallic Cu-Ni/TiO2 nanoparticles. The best performing Cu-Ni/TiO2 photocatalyst has 9 : 1 Cu : Ni mass composition and calcined at 180°C giving 100% Orange II removal with 16.1 ppm TOC value	[84]
Cu-Ni	Electrodeposition	bimodal size distribution 20 to 30 (Ni NPs) and 100	Nickel nanoparticles possess a ball-flower structure, leading to a large specific surface area. In addition, copper interlayer enhanced the conductivity of substrate and showed a synergistic effect with Ni, which enhanced the rate of electron transfer process	[85]
Cu-Ni	Incipient wetness technique/precipitation	1 to 10	The properties of bimetallic alloy particles were investigated. It was found that the presence of Cu greatly enhanced the reducibility of the Ni species and about 85% of the particles were metallic. After initial reduction, many nanoparticles quickly nucleated on the grain boundaries or surface defects of the titania supports. The nanoparticles grew rapidly via the Ostwald ripening or short-range particle-particle coalescence mechanisms	[86]