Fabrication of Metal‐Nanoparticle‐Modified Semiconducting Copper– and Silver–TCNQ Materials as Substrates for the Reduction of Chromium(VI) Using Thiosulfate Ions at Ambient Temperature

Abstract

The formation of readily recoverable and reusable organic semiconducting Cu‐ and AgTCNQ (TCNQ=7,7,8,8‐tetracyanoquinodimethane) microstructures decorated with Pt and Pd metallic nanoparticles is described for the effective reduction of CrVI ions in aqueous solution at room temperature using both formic acid and an environmentally friendly thiosulfate reductant. The M‐TCNQ (M=metal) materials were formed by electrocrystallisation onto a glassy carbon surface followed by galvanic replacement in the presence of H2PtCl6 or PdCl2 to form the composite material. It was found that loading of the surface with nanoparticles could easily be controlled by changing the metal salt concentration. Significantly, the M‐TCNQ substrates facilitated the formation of well‐isolated metal nanoparticles on their surfaces under appropriate galvanic replacement conditions. The semiconductor–metal nanoparticle combination was also found to be critical to the catalyst performance, wherein the best‐performing material was CuTCNQ modified by well‐isolated Pt nanoparticles with both formic acid and thiosulfate ions as the reductant.

Galvanic Replacement of Semiconducting CuTCNQF 4 with Ag + Ions to Enhance Electron Transfer Reaction

“…The beneficial effect on the interfacial charge transport properties is well known when metals are decorated on semiconductors or doped within the lattice of semiconductors ,,. Some of the previous work on CuTCNQ decoration with Au and Ag has already shown enhanced photocatalytic and electronic properties . In addition, we recently showed the ability of CuTCNQF 4 for efficient removal of hexavalent chromium .…”

“…Organic charge transfer complexes based on 7,7,8,8‐tetracyanoquinodimethane (TCNQ) has been a subject of intense research due to their unique properties, along with a resurgence in the interest over the past few years through the pioneering work of Dunbar et al ., Miller et al ., and Bond et al . A breadth of metal‐organic semiconducting complexes (MTCNQ) have been reported, with wide‐spread applicability in data storage,, sensors, electronic devices,,,,, catalysts, and antibacterial agents . Interestingly, the last decade has seen a rise in the use of the fluorinated analogue of TCNQ viz .…”

“…2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (TCNQF 4 ) due to its superior optical, electrical, and magnetic properties in comparison to TCNQ‐based charge transfer complexes ,. Although the fluorinated analogues were primarily explored for field emission and switching devices, recent work by our group and others have shown the potential of MTCNQF 4 (where M=Cu or Ag) to be used as catalysts for electron transfer reactions between ferricyanide and thiosulfate, as well as for the conversion of Cr 6+ to Cr 3+ reduction in the presence of methanol as electron donor ,. To date, much of the work on TCNQ and TCNQF 4 ‐based materials has focused on exploring the applicability of the pristine MTCNQ complex.…”

“…This strategy was primarily shown for the fabrication of bimetallic colloids. Recent efforts by our group and others have expanded the use of this approach for the fabrication of M/CuTCNQ (M=Au, Pt and Pd), M/AgTCNQ (M=Au, Pt and Pd) and CuTCNQ/AgTCNQ hybrid materials ,. Although it is well‐known that the fluorinated analogue has superior properties than pristine TCNQ, the use of GR for the decoration of MTCNQF 4 with noble metals has not been intensively investigated.…”

Manganese-phosphomolybdate molecular catalysts for the electron transfer reaction of ferricyanide to ferrocyanide

“…The as-prepared Au@IFMC-100 microtubes exhibit enhanced catalytic performance for the reduction of K 3 Fe(CN) 6 with NaBH 4 in aqueous solution. 30 During our course of catalytic experiments, the POM-based supramolecular frameworks maintained higher catalytic activity and structural stability. The development of a catalytic material that could utilize thiosulphate as a reductant for the electron transfer reaction would have signicant environmental benets.…”