Pumice is a porous volcanic rock containing a significant proportion of silica and alumina, and which has a low iron content. This natural, silica-rich material attracts wide attention because of its applications in adsorption processes, heterogeneous catalysis and nanotechnology. In this contribution, the white amorphous silica nanoparticles were extracted using an optimized alkaline treatment and an acid-precipitation process using grey pumice powder. The isolated amorphous silica SiO₂ was characterized via X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Transmission Electronic Microscopy (TEM-EDS), N₂ adsorption/desorption measurements and simultaneous Thermal Gravimetry/Differential Thermal Analysis (TG/DTA). The obtained results indicated that the nanosilica powder was successfully prepared via the acid-base route with a predominantly amorphous mesoporous structure having a high surface area (422m²/g). The TEM images exhibited relatively homogeneous dispersed nanosilica particles with small sizes about 5–15 nm, in accordance with XRD data. Thermal analysis of the silica powder under air atmosphere showed total mass losses of 6.5%, with endothermic effects corresponding to the removal of water molecules and the OH of silanol groups contained in the material. The investigations performed in this work have indicated that there is great scope for pumice exploitation as a raw material in the production of amorphous silica nanopowder on large scale.

In this study, novel polyaniline-coated perovskite nanocomposites (PANI@CoTiO₃ and PANI@NiTiO₃) were synthesized using an in situ oxidative polymerization method and evaluated for the photocatalytic degradation of Rhodamine B (RhB) a persistent organic pollutant. The nanocomposites displayed significantly enhanced photocatalytic efficiency compared to pure perovskites. The 1%wt PANI@NiTiO₃ achieved an impressive 94% degradation of RhB under visible light after 180 min, while 1wt.% PANI@CoTiO3 reached 87% degradation under UV light in the same duration. X-ray diffraction (XRD) confirmed that the crystalline structures of CoTiO₃ and NiTiO₃ remained intact post-polymerization. At the same time, Fourier transform infrared spectroscopy (FTIR) verified the successful deposition of PANI through characteristic functional group vibrations. Diffuse reflectance spectroscopy (DRS) revealed reduced band gaps of 2.63 eV for 1wt.% PANI@NiTiO₃ and 2.46 eV for 1wt.% PANI@CoTiO₃, enhancing light absorption across UV and visible ranges. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analysis demonstrated the uniform distribution of PANI, ensuring consistent surface activity and efficient charge transfer. The photocatalytic test confirmed a pseudo-first-order degradation mechanism. The study elucidates the degradation mechanism through intermediate identification via HPLC-MS analysis, highlighting N-de-ethylation, aromatic ring cleavage and eventual mineralization into CO₂ and H₂O as critical pathways. Furthermore, the 1wt.%PANI@NiTiO₃ nanocomposite demonstrated excellent stability and recyclability, maintaining its degradation efficiency over four consecutive cycles with minimal change. These findings highlight the potential of PANI@XTiO₃ nanocomposites for sustainable and efficient wastewater treatment, addressing diverse environmental challenges by tailoring photocatalysts to specific light sources.

Photocatalyzed degradation of phenol in aqueous solution over surface impregnated TiO₂ (M = Cu, Cr, V) under UV-Vis (366 nm) and UV (254 nm) irradiation is described. Nanosized photocatalyts were prepared from TiO₂-P25 by wet impregnation, and characterized by X-ray diffraction, X-ray fluorescence, transmission electron microscopy, UV-Vis diffuse reflectance spectroscopy, Raman spectroscopy, and adsorption studies. No oxide phases of the metal dopants were found, although their presence in the TiO₂-P25 lattice induces tensile strain in Cu-impregnated TiO₂-P25, whereas compressive strain in Cr- and V-impregnated TiO₂-P25. Experimental evidences support chemical and mechanical stability of the photocatalysts. Type IV N₂ adsorption–desorption isotherms, with a small H3 loop near the maximum relative pressure were observed. Metal surface impregnated photocatalysts are mesoporous with a similar surface roughness, and a narrow pore distribution around ca. 25 Å. They were chemically stable, showing no metal lixiviation. Their photocatalytic activity was followed by UV-Vis spectroscopy and HPLC–UV. A first order kinetic model appropriately fitted the experimental data. The fastest phenol degradation was obtained with M (0.1%)/TiO₂-P25, the reactivity order being Cu > V >> Cr > TiO₂-P25 under 366 nm irradiation, while TiO₂-P25 > Cu > V > Cr, when using 254 nm radiation. TOC removal under 366 nm irradiation for 300 min showed almost quantitative mineralization for all tested materials, while 254 nm irradiation for 60 min led to maximal TOC removal (ca. 30%). Photoproducts and intermediate photoproducts were identified by HPLC–MS, and appropriate reaction pathways are proposed. The energy efficiency of the process was analysed, showing UV lamps are superior to UVA lamps, and that the efficiency of the surface impregnated catalyst varies in the order Cu > V > Cr.