Defect-Tailoring and Titanium Substitution in Metal–Organic Framework UiO-66-NH₂ for the Photocatalytic Degradation of Cr(VI) to Cr(III)

Abstract

Defect engineering and surface chemistry are closely related to the performance of materials. In this work, the effects of Zr precursors and Ti substitution on the photocatalytic performance of UiO-66-NH 2 are studied and analyzed from the perspective of defect engineering and surface chemistry. The findings show that when using ZrOCl 2 •8H 2 O as the Zr precursor combined with the postsynthetic treatment of Ti substitution, sample U-OCl-Ti shows significant improvement in Cr(VI) adsorption (20.9 mg/g) and photocatalytic reduction of Cr(VI) under visible light. The improvement can be attributed to the highly defective framework and more -NH 2 groups exposed on the surface; therefore the highest light absorption and lowest recombination rate of photogenerated electron−hole pairs are observed in U-OCl-Ti. The findings in this study contribute to a better understanding of how defects and surface chemistry affect the photocatalytic performance, thus providing some designing knowledge for the synthesis of UiO-66 or UiO-66-NH 2 with high photocatalytic performance.

Chromium Speciation in Zirconium‐Based Metal–Organic Frameworks for Environmental Remediation

“…The UiO-66-NH 2 sample was also subjected to aC r VI to Cr III photo-reduction under UVAa nd visible light illumination. The main goal of the Cr VI photo-reduction experimentsi sn ot only to prove the feasibility of UiO-66-NH 2 samples to phototransform chromate species, since this has been previously corroborated by several research teams, [6,70,71] but to latter compare the chromium speciation stabilized within UiO-66-NH 2 material after operation. To this end, the photo-reduction experiments were performed under ultraviolet and visible light irradiation over a5ppm chromate solutionw ith ap hotocatalyst loading of 0.25 gL À1 .T he photo-reduction curvess hown in Figure S7 confirm that all the chromate speciesh aveb een reduced to Cr III when the materiali se xposed to UVAr adiation, and nearly the 80 %o ft he chromate is transformed to Cr III under visible illumination.…”

Modulation of the Bifunctional CrVI to CrIII Photoreduction and Adsorption Capacity in ZrIV and TiIV Benchmark Metal-Organic Frameworks

“…Therefore, efficient light harvesting [21], semiconducting nature [22], porosity [23][24][25], and chemical affinity to capture the transformed species are some of the key characteristics that need to be specifically encoded within the desired bifunctional catalyst [25]. Classic metal-oxide photocatalysts exhibit excellent photodegradation activities over a variety of pollutants, but their capacity to adsorb or retain the photodegradation intermediates and products is limited by its reduced porosity and surface areas [26][27][28][29]. In this context, metal-organic frameworks (MOFs) stand out as highly porous materials that are able to meet photoactivity and porosity.…”

“…In this context, metal-organic frameworks (MOFs) stand out as highly porous materials that are able to meet photoactivity and porosity. MOFs can be formed from semiconductor metal-oxide clusters and efficient light-harvesting organic linkers assembled in extended and ordered porous structures [27,30]. The combination of these two characteristics, together with the possibility to further decorate or engineer their structures, both pre and post synthetically, make MOFs the ideal candidates to combine photoreduction and adsorption properties [21,[31][32][33].…”

Defect Engineering in Metal‒Organic Frameworks as Futuristic Options for Purification of Pollutants in an Aqueous Environment

“…FIGURE 10 | (A) UiO-66-NH 2 (Ti) photocatalytic degradation Cr (VI) under visible light(Feng et al, 2019). (B) Mechanism of Cr (VI) reduction under visible light with defect UiO-66(Chen et al, 2019).…”