Although, plenty of photocatalytic approaches have been developed in the past few decades to overcome major drawbacks, such as; wide band gap and fast volume/surface recombination of the charge carriers, the researchers still need to carry out careful systematic studies before conducting experiments based on physicochemical properties of a system. Thus, in this review, a detailed discussion of the band edge positions controlling the migration and charge separation of the produced charged carriers and its impact onto the photocatalytic systems are provided. The knowledge of band edge positions is a crucial prerequisite to a rational design of an efficient photocatalytic system. The enhancement mechanism should match these criteria to be reliable in the field of heterogeneous photocatalysis science.

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Bismuth basic nitrate (BBN) and its TiO2-Ag modified sorbent, PTBA were successfully synthesized via a precipitation method. The structural characteristics of prepared sorbents were determined through different analytical techniques. The potential use of prepared sorbents for organic compounds' removal was evaluated using Methyl Orange and Sunset Yellow dyes as model pollutants in aqueous solutions. The experimental results showed that the presence of TiO2and Ag particles during the crystal growth of bismuth basic nitrate has an effect on the crystal structure, point of zero charge (pHpzc), pore volume and diameter. The lower binding energy of Ti 2p core level peak indicates the octahedral coordination of TiO2particles on the PTBA surface. The alteration of hydrophilic-hydrophobic characteristics of sorbent's surface improves the adsorptive performance of the modified sorbent and provides an efficient route for organic contaminants' removal from aqueous solutions.

This paper presents the synthesis of penta-bismuth hepta-oxide nitrate, Bi5O7NO3, via the chemical precipitation method. After calcination, the precipitate was characterised by several methods, which included X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy, Fourier transform infrared, thermogravimetric analysis, BET surface area and pH drift method to determine the pH of point of zero charge (pHpzc). The study results revealed that Bi5O7NO3had an orthorhombic crystal structure, a surface area of 1.6 m2 g-1 and a point of zero charge at pH 9.7. The chemical state of Bi5O7NO3indicated the presence of three oxidation states of bismuth centre. Furthermore, the decolourization ability of Bi5O7NO3to remove the azo dye was also evaluated. Although it had lower surface area, the removal efficiency was extremely good. This finding suggests that Bi5O7NO3could be used as a promising adsorbent for azo dye removal. The XPS spectra showed that the accumulation of dye onto Bi5O7NO3could be due to the anion exchange process, suggesting the birth of a new anion exchanger for azo dye removal.

The adsorption of methyl orange dye from aqueous solution onto penta-bismuth hepta-oxide nitrate, Bi(5)O(7)NO(3), synthesized by precipitation method, was studied in a batch adsorption system. The effects of operation parameters such as adsorbent dose, initial dye concentration, pH and temperature were investigated. The adsorption equilibrium and mechanism of adsorption was evaluated by Langmuir and Freundlich isotherm and different kinetic models, respectively. The results indicate that adsorption is highly dependent on all operation parameters. At optimum conditions, the adsorption capacity was found to be 18.9 mg/g. The adsorption data fits well with the Langmuir isotherm model indicating monolayer coverage of adsorbate molecules on the surface of Bi(5)O(7)NO(3). The kinetic studies show that the adsorption process is a second-order kinetic reaction. Although intra-particle diffusion limits the rate of adsorption, the multi-linearity plot of intra-particle model shows the importance of both film and intra-particle diffusion as the rate-limiting steps of the dye removal. Thermodynamic parameters show that the adsorption process is endothermic, spontaneous and favourable at high temperature.