Nanosized ZrO₂ powders with near pure monoclinic, tetragonal, and cubic structures synthesized by various methods were used as catalysts for photocatalytic degradation of methyl orange. The structural and textural properties of the samples were analyzed by X-ray diffraction, Raman spectroscopy, TEM, UV-vis, X-ray photoelectron spectroscopy (XPS), and N₂ adsorption measurements. The performance of synthesized ZrO₂ nanoparticles in the photocatalytic degradation of methyl orange under UV light irradiation was evaluated. The photocatalytic activity of the pure monoclinic ZrO₂ sample is higher than that of the tetragonal and cubic ZrO₂ samples under optimum identical conditions. The characterization results revealed that monoclinic ZrO₂ nanoparticles possessed high crystallinity and mesopores with diameter of 100 Å. The higher activity of the monoclinic ZrO₂ sample for the photocatalytic degradation of methyl orange can be attributed to the combining effects of factors including the presence of small amount of oxygen-deficient zirconium oxide phase, high crystallinity, large pores, and high density of surface hydroxyl groups.

TiO2 nanoparticles were synthesized from titanium isopropoxide by a simple peptization method using sulfuric, nitric, and acetic acids. The effect of peptizing acid on physicochemical and photocatalytic properties of TiO2 powders was studied. The structural properties of synthesized TiO2 powders were analyzed by using XRD, TEM, N2-physisorption, Raman, DR UV-vis, FTIR, and X-ray photoelectron spectroscopy techniques. The characterization results showed that acetic acid peptization facilitated the formation of pure anatase phase after thermal treatment at 500 °C; in contrast, nitric acid peptization led to a major rutile phase formation (67%). Interestingly, the sample peptized using sulfuric acid yielded 95% anatase and 5% rutile phases. The photocatalytic activity of synthesized TiO2 nanoparticles was evaluated for degradation of selected organic dyes (crystal violet, methylene blue, and p-nitrophenol) in aqueous solution. The results confirmed that the TiO2 sample peptized using nitric acid (with rutile and anatase phases in 3:1 ratio) offered the highest activity for degradation of organic dyes, although, TiO2 samples peptized using sulfuric acid and acetic acid possessed smaller particle size, higher band gap energy, and high surface area. Interestingly, TiO2 sample peptized with nitric acid possessed relatively high theoretical photocurrent density (0.545 mAcm−2) and pore diameter (150 Å), which are responsible for high electron-hole separation efficiency and diffusion and mass transportation of organic reactants during the photochemical degradation process. The superior activity of TiO2 sample peptized with nitric acid is due to the effective transfer of photogenerated electrons between rutile and anatase phases.

TiO ₂ with different ratios of anatase/rutile phases were synthesized via a microwave assisted sol–gel method and by applying a single source precursor (SSP) with a constant concentration of nitric acid that was used as the structure directing agent.

Mesoporous CuO-ZrO₂ catalysts were prepared and calcined at 500 °C. The performance of the synthesized catalysts for benzylation of benzene using benzyl chloride was studied. The bare support (macroporous ZrO₂) offered 45% benzyl chloride conversion after reaction time of 10 h at 75 °C. Significant increase in benzyl chloride conversion (98%) was observed after CuO loading (10 wt. %) on porous ZrO₂ support. The conversion was decreased to 80% with increase of CuO loading to 20 wt. %. Different characterization techniques (XRD, Raman, diffuse reflectance UV-vis, N₂-physisorption, H₂-TPR, XPS and acidity measurements) were used to evaluate physico-chemical properties of CuO-ZrO₂ catalysts; the results showed that the surface and structural characteristics of the ZrO₂ phase as well as the interaction between CuO-ZrO₂ species depend strongly on the CuO content. The results also indicated that ZrO₂ support was comprised of monoclinic and tetragonal phases with macropores. An increase of the volume of monoclinic ZrO₂ phase was observed after impregnation of 10 wt. % of CuO; however, stabilization of tetragonal ZrO₂ phase was noticed after loading of 20 wt. % CuO. The presence of low-angle XRD peaks indicates that mesoscopic order is preserved in the calcined CuO-ZrO₂ catalysts. XRD reflections due to CuO phase were not observed in case of 10 wt. % CuO supported ZrO₂ sample; in contrast, the presence of crystalline CuO phase was observed in 20 wt. % CuO supported ZrO₂ sample. The mesoporous 10 wt. % CuO supported ZrO₂ catalyst showed stable catalytic activity for several reaction cycles. The observed high catalytic activity of this catalyst could be attributed to the presence of a higher number of dispersed interactive CuO (Cu²⁺-O-Zr⁴⁺) species, easy reducibility, and greater degree of accessible surface Lewis acid sites.