Heterogeneous
photocatalysis has captured worldwide attention because
of its tremendous potential in the field of solar energy conversion
to solve energy and environmental issues. Efficient utilization of
solar energy is always the target of our pursuit in the areas of photocatalysis.
The design of appropriate photocatalysts for wide-range light harvest
from ultraviolet to near-infrared regions is a promising way to realize
the practical utilization of photocatalysis. To date, the exploration
of NIR light-responsive photocatalysis includes sensitization with
near-infrared light (NIR) responsive materials such as dye molecules
and black phosphorus, the surface plasmon resonance effect, upconversion,
and narrow band gap materials as NIR harvesters. This review gives
a comprehensive discussion and summary on the latest developments
of the design and engineering of NIR-active photocatalysts and the
related photocatalytic system for various environmentally friendly
photoreactions including environmental remediation, water splitting,
CO2 reduction, nitrogen fixation, and selective organic
transformations. Finally, the future perspectives and challenges are
present at the end in order to give a comprehensive understanding
about the present near-infrared-driven photocatalysis and the promising
directions for future investigations.
Aqueous hexavalent chromium (Cr(VI)) treatment and chromium resource recovery toward Cr-containing wastes are of significant importance and necessity to both wastewater remediation and resource recovery. Herein, via mild photoreaction conditions with isopropanol (IPA) as an electron donor, a catalystfree strategy for aqueous Cr(VI) extraction to form an insoluble polyhydroxy Cr(V) complex is developed for the first time. Aqueous Cr(VI) with concentration from 5 to 150 ppm can be efficiently extracted with high selectivity even in the presence of coexisting ions, and the total Cr concentration in residue solution can be as low as 0.5 ppm. The Cr resource could be efficiently recovered as pure Cr 2 O 3 by calcinating the resulting Cr(V) precipitate. Outstanding extraction efficiency could be realized with various IPA concentrations (1.3−12.0 mol/L) by coordinately tuning the pH value to promote the formation of Cr(VI)-IPA ester. The formed ester undergoes intramolecular electron transition under visible light irradiation, resulting in a polyhydroxy solid-state Cr(V) intermediate complex. The controlled pH value blocks further reduction of Cr(V) to soluble Cr(III); thus the insoluble Cr(V) intermediate complex is stabilized thermodynamically under ambient conditions. Because of its electric neutrality property and the strong intermolecule interaction via hydrogen bonds, a dioxobridged di-nuclear Cr(V) complex {Cr 2 (μ-O) 2 (OH) 4 [OCH(CH 3 ) 2 ] 2 } is finally precipitated as the main product. Satisfactory extraction and recovery of Cr from chromium-plating wastewater and discarded stainless steel verify that this approach is ideal for both one-step purification of Cr(VI)-containing wastewater and selective resource recovery from Cr-containing solid wastes in practical application.
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