Copper hexacyanoferrate nanocrystal as a highly efficient non-noble metal catalyst for reduction of 4-nitrophenol in water.

As Prussian Blue analogues (PBAs) represent one of the most classical families of coordination compounds and exhibit versatile catalytic activities, PBAs have been considered as useful heterogeneous catalysts for reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). Nevertheless, while Cu has been a well-proven transition metal for 4-NP reduction, especially, due to their ability to attain pronounced conversions of reactants under mild conditions, environmental friendliness and great stability. Nevertheless, while Cu has been a well-proven transition metal for 4-NP reduction, Cu-based PBA has never been developed and thoroughly investigated for 4-NP reduction. Thus, in this study, copper hexacyanoferrate, CuII3[Fe(CN)6]2 (CuFeCN) is particularly synthesized and proposed for the first time as a catalyst for reduction of 4-NP in the presence of NaBH4. CuFeCN exhibits a very high catalytic activity towards reduction of 4-NP to 4-AP with 100% conversion within 4 min. The activity factor (AF) at room temperature, 8057.14 s-1 g-1, is between 1 and 2 orders higher than all other MFeCN Prussian blue analogues (M = Co, Fe, Ni, Zn, and Mn). In addition, CuFeCN shows excellent reusability to achieve 100% conversion of 4-NP to 4-AP with highly stable rate constants over successive 7 cycles. The activation energy (Ea) and turn over frequency (TOF) for the reduction of 4-NP to 4-AP catalyzed by CuFeCN system are determined as 24.6 kJ mol-1 and 36.93 min-1, respectively, which are both significantly more superior than most of reported catalysts in literatures. These advantageous properties make CuFeCN ideal to be developed into a promising catalyst for elimination of nitroaromatic contaminants in water.

ZIF-67 supported on marcoscale resin as an efficient and convenient heterogeneous catalyst for Oxone activation.

While metal organic frameworks (MOFs) are promising catalysts for aqueous chemical oxidation, MOFs are typically prepared to be nanoscale and thus less practical for solution-based reactions. Although a few attempts have developed substrate-supported MOFs, many of them are still small and none of them are developed for sulfate-radical based chemical oxidation. However, there is still an urgent demand for developing substrate-supported MOFs which are catalytically effective, conveniently prepared, and simply recyclable. In this study, a macrosphere-supported MOF is successfully fabricated using ion exchange resins as readily available, stable and functionalized macrospheres. Via equilibrating resins with 2-MIM and cobalt ions sequentially, a cobalt-based MOF, zeolitic imidazolate framework-67 (ZIF-67) nanocrystal, is grown on the resin surface via self-assembly. The resulting composite of ZIF "at" resin (abbreviated as ZIF@R) can preserve porous structures and metal coordination of ZIF-67, and also convenient features of resins, making it an advantageous heterogeneous catalyst for activating Oxone in water. As Rhodamine B (RhB) decolorization is employed as a model test for evaluating Oxone activation, ZIF@R is confirmed not only to activate Oxone for full decolorization of RhB but also to exhibit a much higher catalytic activity than Co3O4, the most typical catalyst for Oxone. ZIF@R could be also re-used to activate Oxone for RhB decolorization without activity loss. These results indicate that ZIF@R is a conveniently prepared and highly effective and stable macroscale catalyst for aqueous chemical oxidation reactions.

Elimination of bromate from water using aluminum beverage cans via catalytic reduction and adsorption.

While zero valent aluminum (ZVAl) is a promising reductant for eliminating bromate from water, ZVAl is typically obtained from reagent grade aluminum. As used aluminum beverage can is the most common aluminum waste, it can be conveniently used to prepare ZVAl. Thus, in this study aluminum beverage cans are employed for the first time as a plentiful and easily accessible aluminum source to afford ZVAl for eliminating bromate from water. As aluminum is easily oxidized to form aluminum oxide, aluminum can pieces (ACPs) are pre-treated with HCl for removing the oxide layer to afford ZVAl. While non-acid-treated ACP is ineffective to remove bromate, the acid-treated ACP successfully eliminates bromate from water completely. Bromate elimination by ACP is attributed to reduction of bromate to bromide by the reactive sites of ACP and adsorption of bromate to the surface of ACP. Bromate elimination by ACP also proceeds much faster at higher temperatures and low pH values, while the alkaline condition causes serious negative effects on bromate elimination. Besides, oxalic acid is found to facilitate bromate elimination not only on the kinetics but also reduction to bromide because the passivation layer is suppressed in the presence of oxalic acid. ACP could also be reused and the acid-washing regeneration could enable used ACP to restore its reactive sites for bromate elimination. This study successfully demonstrates the valorization of aluminum beverage cans for mitigating the toxic bromate and the findings here provide useful information and insights to develop aluminum beverage cans for controlling pollutants in water.

Prussian Blue analogue supported on sulfur-doped carbon nitride as an enhanced heterogeneous catalyst for activating peroxymonosulfate.

While Prussian Blue (PB) analogues are attractive catalysts for activating peroxymonosulfate (PMS), PB analogues are very small and thus difficult for recovery. Immobilizing PB particles onto graphene is a useful technique which facilitates recovery and also enhances catalytic activities. As doping graphene with sulfur/nitrogen (S/N) increases its electro-conductivity and active sites, the composite of PB and S/N-doped graphene should enhance PMS activation. Thus, this study aims to fabricate such a composite. Unlike conventional S/N-doped graphene prepared via post-modifications, trithiocyanuric acid is used as a precursor, which is converted to S-doped graphitic carbon nitride (SCN). The composite of PB and SCN (PBSCN) is then fabricated by growing a cobalt-based PB analogue on SCN. The resulting PBSCN preserves the crystalline structures, textural properties and catalytic sites of PB and SCN. As degradation of Acid Red 27 (AR) is used as a model reaction, PBSCN exhibits a higher catalytic activity than PB and SCN individually, as well as Co3O4 to activate PMS for AR degradation possibly because SCN may facilitate electron transfer and enhance catalytic activities of PB. PBSCN also remains effective and re-usable over several cycles for AR degradation. These features indicate that PBSCN is a promising catalyst for activating PMS and the fabrication technique demonstrated here can be employed to prepare composites of various PB analogues and carbon nitride to exhibit enhanced catalytic activities.