Cr(VI) remediation from aqueous environment through modified-TiO₂-mediated photocatalytic reduction

Abstract

Cr(VI) exhibits cytotoxic, mutagenic and carcinogenic properties; hence, effluents containing Cr(VI) from various industrial processes pose threat to aquatic life and downstream users. Various treatment techniques, such as chemical reduction, ion exchange, bacterial degradation, adsorption and photocatalysis, have been exploited for remediation of Cr(VI) from wastewater. Among these, photocatalysis has recently gained considerable attention. The applications of photocatalysis, such as water splitting, CO2 reduction, pollutant degradation, organic transformation reactions, N2 fixation, etc., towards solving the energy crisis and environmental issues are briefly discussed in the Introduction of this review. The advantages of TiO2 as a photocatalyst and the importance of its modification for photocatalytic reduction of Cr(VI) has also been addressed. In this review, the photocatalytic activity of TiO2 after modification with carbon-based advanced materials, metal oxides, metal sulfides and noble metals towards reduction of Cr(VI) was evaluated and compared with that of bare TiO2. The photoactivity of dye-sensitized TiO2 for reduction of Cr(VI) was also discussed. The mechanism for enhanced photocatalytic activity was highlighted and attributed to the resultant properties, namely, effective separation of photoinduced charge carriers, extension of the light absorption range and intensity, increase of the surface active sites, and higher photostability. Advantages and limitations for photoreduction of Cr(VI) over modified TiO2 are depicted in the Conclusion. The various challenges that restrict the technology from practical applications in remediation of Cr(VI) from wastewater were addressed in the Conclusion section as well. The future perspectives of the field presented in this review are focused on the development of whole-solar-spectrum responsive, TiO2-coupled photocatalysts which provide efficient photocatalytic reduction of Cr(VI) along with their good recoverability and recyclability.

Magnetite Functionalized Nigella Sativa Seeds for the Uptake of Chromium(VI) and Lead(II) Ions from Synthetic Wastewater

“…The adsorption of Cr(VI) ions on both adsorbents was lower compared to Pb(II) ions due to electrostatic repulsion of hydroxyl ions which are negatively charged [48]. ) [51][52][53]. The speciation of these Cr(VI) anions depends on the concentration and pH of the solution [54,55].…”

Incorporating nitrogen vacancies in exfoliated B-doped g-C3N4 towards improved photocatalytic ciprofloxacin degradation and hydrogen evolution

“…Semiconductor photocatalysis has attracted enormous attention to mitigate the emerging global energy crisis through generation of green hydrogen energy by water splitting and to solve alarmingly growing environmental issues through degradation of organic pollutants using inexhaustible solar energy as the driving force. [1][2][3][4] The organic polymer graphitic carbon nitride (g-C 3 N 4 ) in its nanostructured form with a low band gap energy of B2.7 eV and an appealing band structure has been regarded as one of the most auspicious next generation visible-light-responsive metal-free photocatalysts in the field of environmental pollution abatement and hydrogen evolution. [5][6][7] Additionally its intriguing properties including chemical inertness, non-toxicity, inexpensiveness, abundant availability and facile fabrication induced ripples of excitement among the research community.…”

Review of advanced sensor devices employing nanoarchitectonics concepts

“…Today, sensors play an important role in technological advancement for various social demands. There are currently many strategies being pursued for the production of functional materials [5–8], the detection of various risks [9–11], environmental remediation including pollution problems [12–14], energy production [15–17], energy and electricity storage [18–20], device technologies [21–23], and biomedical treatment [24–27], and the targets must be detected with high selectivity, high efficiency, environmental friendliness, and with low cost and low emission. Various fundamental areas of science and technology, such as organic synthesis [28–30], supramolecular organization [31–35], physical fabrication [36–38] and biotechnology [39–41], are expected to solve these problems where some additional factors have to be considered in order to achieve a high degree of control over the structure.…”