Herein, a simple approach based on tailoring the surface charge of nanoparticles, NPs, during the preparation to boost the electrostatic attraction between NPs and the organic pollutant was investigated. In this study, chargeable titania nanoparticles (TiΟ2 NPs) were synthesized via a hydrothermal route under different pH conditions (pH = 1.6, 7.0 and 10). The prepared TiΟ2 NPs were fully characterized via various techniques including; transmission electron microscopy (TEM), X-ray diffraction (XRD), N2 adsorption/desorption, X-ray photoelectron spectroscopy (XPS), Ultraviolet–visible spectroscopy (UV-Vis) and dynamic light scattering (DLS). The influence of the preparation pH on the particle size, surface area and band gap was investigated and showed pH-dependent behavior. The results revealed that upon increasing the pH value, the particle size decreases and lead to larger surface area with less particles agglomeration. Additionally, the effect of pH on the surface charge was monitored by XPS to determine the amount of hydroxyl groups on the TiO2 NPs surface. Furthermore, the photocatalytic activity of the prepared TiΟ2 NPs towards methylene blue (MB) photodegradation was manifested. The variation in the preparation pH affected the point of zero charge (pHPZC) of TiO2 NPs, subsequently, different photocatalytic activities based on electrostatic interactions were observed. The optimum efficiency obtained was 97% at a degradation rate of 0.018 min−1 using TiO2 NPs prepared at pH 10.

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Water pollution from the continuous disposal of hazardous substances has become a serious issue and a global concern for the environment and public health. Removal of these pollutants from water is an ongoing challenge, and several approaches have been proposed and applied for this purpose. Adsorption is one of the common and most efficient approaches often used because it is simple, quick processing, inexpensive, and eco-friendly. Polyoxometalates (POMs) are a well-known class of metal–oxygen cluster compounds with tunable structure and size and highly electronegative and oxo-enriched surfaces. Owing to their electronic and physical properties, they have attracted considerable attention in the field of pollutants removal from wastewater. This review discusses the advances made over the last 10 years in the removal of toxic pollutants from wastewater using POMs-based materials. Furthermore, we summarize the recent synthetic strategies used to modify POMs-based materials and their applications in adsorption of pollutants. Knowledge gaps and current challenges in this research area are also discussed to support the development prospect of these materials for industrial use.