Table 2. Comparative analysis of photocatalyst synthesis methods.

Synthesis method	Key features	Advantages	Limitations	Materials synthesized	Photocatalytic applications	Ref.
Sol–gel	Wet-chemical method based on hydrolysis and condensation	Low-cost, good homogeneity, and precise control over composition and morphology	Time-consuming drying and calcination; risk of agglomeration	TiO2, ZnO, WO3, and Fe2O3 composites	Dye degradation, H2 generation, and air/water purification	51
Solvothermal	Uses organic solvents at high temperature and pressure	Excellent crystallinity, tunable shape/morphology, and good for heterostructures	Requires high-pressure autoclaves; limited scalability	TiO2, BiVO4, ZnTiO3, and WO3-based composites	Visible-light photocatalysis, CO2 reduction, and dye degradation	62
Hydrothermal	Water-based, high-temperature/pressure synthesis in sealed vessels	Eco-friendly, high purity, and suitable for nanorod/sheet structures	Long synthesis time, batch limitation, and poor in situ monitoring	TiO2, ZnO, WO3, MOFs, and g-C3N4 composites	Water disinfection, dye degradation, and photocatalytic H2 evolution	70
Co-precipitation	Simultaneous precipitation of multiple ions in solution	Simple, scalable, low-temperature synthesis, and homogeneous doping	Poor crystallinity without post-annealing; possible phase separation	TiO2/Fe, ZnO, ZrO2, MOFs, and ternary oxides	Organic dye degradation; pharmaceutical removal	77
Chemical vapor deposition	Gas-phase deposition via precursor reaction on a heated substrate	High-purity, conformal thin films, and atomic-level thickness control	Requires high temp & vacuum systems and costly precursors	TiO2, ZnO, TiO2 – CNT -Ag, and WO3	Self-cleaning surfaces, NOx removal, and solar fuel cells	90
Microwave	Rapid heating via microwave irradiation	Fast synthesis, uniform particle formation, and energy-efficient	Difficulty in scaling, hot spot formation, and limited control over particle growth	ZnO, TiO2, g-C3N4, MOFs, and graphene composites	Dye degradation, antibiotic removal, and H2 evolution	100
Ultrasonic	Cavitation-based synthesis using high-frequency ultrasound	Room temperature, rapid mixing, and better dispersion and crystallinity	Particle size variability; potential contamination from probe materials	TiO2, ZnO, MOFs, and rGO nanocomposites	Visible-light catalysis, antibacterial surfaces, and dye degradation	109
Electrochemical	Electrodeposition or anodization from ionic precursors	Precise thickness control, low temp, and strong adhesion on substrates	Limited to conductive substrates; sensitive to deposition parameters	TiO2/ZnO, Ag/ZnO, and graphene–ZnO composites	Photo-electrochemical water splitting and dye removal	120
Mechanochemical	Solvent-free synthesis via mechanical grinding or milling	Green, scalable, energy-efficient, and induces defects and doping	Limited control over uniformity and equipment contamination risk	TiO2, ZnO, Fe2O3, and biochar composites	UV/solar-light degradation; antibiotic removal	127
Ionothermal	Uses ionic liquids as solvents and structure-directing agents	Solvent-free, tunable porosity, and high crystallinity	Cost of ILs; residual IL removal challenges	MOFs, TiO2/IL composites, and Fe/Zn MOFs	CO2 reduction, dye degradation, and solar fuels	137
Microemulsion	Nanoscale reactors formed from water-oil-surfactant systems	Narrow size distribution; morphology control at room temperature	Complicated formulation; surfactant removal post-synthesis	ZnO, TiO2, CdS, and Ag-based quantum dots	Dye degradation, hydrogen evolution, and photocatalytic sensors	141
Atomic layer deposition	Layer-by-layer gas-phase deposition via surface-limited reactions	Atomic precision, ultra-thin conformal coatings, and excellent interfacial tuning	Slow deposition rate; expensive instrumentation	TiO2, Fe2O3/TiO2, and ZnO films	Heterojunctions for H2 generation; visible-light catalysis	146
Green synthesis	Biogenic route using plant extracts, microbes, or algae	Eco-friendly, low-cost, biocompatible, and avoids toxic reagents	Reproducibility issues, purification complexity, and slow reaction rates	TiO2, ZnO, CeO2, SnO2, and MOFs via plant/bacterial extracts	Antibacterial coatings, dye degradation, and water treatment	155