Visible-Light-Driven Zr-MOF/BiOBr Heterojunction for the Efficient Synchronous Removal of Hexavalent Chromium and Rhodamine B from Wastewater

Abstract

With the rapid industrial development, the coexistence of multiple pollutants in wastewater has become a common phenomenon. Thus, developing highly efficient decontamination methods is imperative. In this work, a string of UiO-66-NH 2 /BiOBr heterojunctions with varying ratios of BiOBr were prepared and applied to remove hexavalent chromium Cr(VI) and rhodamine B (RhB). The possible growth process of BiOBr nanosheets on UiO-66-NH 2 , removal activity of contaminants, and photocatalysis mechanism were investigated. When the mass ratio of UiO-66-NH 2 to BiOBr reaches 1:0.75, the heterojunction (NB-75) shows optimal photocatalytic activity. After 30 min of adsorption, the total removal rates of Cr(VI) (50 mg/L) and RhB (10 mg/L) over NB-75 (0.25 g/L) reaches 96.7% within 120 min of illumination and 98.9% within 80 min of illumination, respectively. For the removal process, there are two factors. The first is the high adsorption capacity for RhB and Cr(VI) owing to the high porosity of UiO-66-NH 2 and interlayer surface positive charge of BiOBr. The second is the improved visible-light photocatalytic performance of the UiO-66-NH 2 /BiOBr heterojunction via rapid separation of photoinduced carriers. In addition, the active species capture study reveals that the electrons (e – ) and the superoxide radicals ( • O 2 – ) play key roles in Cr(VI) reduction, while the holes (h + ) are major reactive groups participating in the degradation of RhB. This work demonstrated a kind of promising MOF-based photocatalysis material for eliminating Cr(VI) and RhB simultaneously.

Fabrication of Cu-MOF-Derived Cu/CuxO/C Bifunctional Materials for Light and Dark Catalytic Properties

“…As shown in the Mott−Schottky (M−S) curve in Figure 9c, the positive slope of Cu/Cu x O-1 indicates that it is an n-type semiconductor with a flat-band potential of −1.58 V relative to Ag/AgCl (−1.37 V relative to NHE). 65 Typically, the conduction band (CB) potential is about 0.10 V more negative than the flat-band potential of n-type semiconductors. The CB potential for Cu/Cu x O-1 is thus calculated to be −1.47 eV.…”

Photoelectroactive metal–organic frameworks

“…Photodegradation of rhodamine B (RhB) (Scheme 4) is one of the major concerns in wastewater treatment. 72,107,[181][182][183][184][185][186] . 182 The photodegradation of methylene blue (MB) (Scheme 4) is another concern in wastewater treatment.…”

“…Photodegradation of rhodamine B (RhB) (Scheme 4) is one of the major concerns in wastewater treatment. 72,107,181–186 For instance, a pristine MOF {[Cu(tpt)]·3H 2 O·0.5SO 4 } n constructed from CuSO 4 ·5H 2 O and 2,4,6-tris(4-pyridyl)-1,3,5-triazine (tpt) demonstrated aqueous RhB (20.0 mg L −1 ) degradation in the presence of 30% H 2 O 2 at room temperature under visible light LED irradiation, with a degradation efficiency of 77% and a rate constant of 2.10 × 10 −2 min −1 within 70 min involving the generation of active species of ˙OH. 72 In another case, SNNU-110 constructed from In(NO 3 ) 3 · x H 2 O and 4,4′,4′′- s -triazine-1,3,5-triyltri- p -aminobenzoic acid showed a degradation efficiency of 94.6% for aqueous sulforhodamine B within 70 min at ambient temperature under xenon lamp irradiation.…”

Dual-Functional Ln-OFs for Efficient Luminescence Sensing and Photoreduction of Cr(VI) without Additional Photosensitizers and Cocatalysts

“…The luminescent detection of Cr 2 O 7 2– in aqueous solution is the first step, and the removal of Cr­(VI) from wastewater is the real ultimate goal. Many methods are often employed to remove Cr­(VI), such as electrochemical reduction, ion exchange, adsorption, and photocatalytic removal. − Since the Cr­(III) ion is less toxic and easily precipitated in the solid state, the conversion of Cr­(VI) to Cr­(III) is a rapid method to remove highly toxic chromium . The photocatalytic reduction method has many benefits, such as cost effectiveness, simplicity, environment-friendliness, and recyclability .…”

“…31−34 Since the Cr(III) ion is less toxic and easily precipitated in the solid state, the conversion of Cr(VI) to Cr(III) is a rapid method to remove highly toxic chromium. 31 The photocatalytic reduction method has many benefits, such as cost effectiveness, simplicity, environment-friendliness, and recyclability. 35 Nowadays, many semiconductors, such as TiO 2 , ZnO, CdS, α-Fe 2 O 3 , CdS, SnS 2 , and Ag 2 S, have been used to photocatalytically reduce Cr(VI).…”