Synthesis and characterization of Co/Ti layered double hydroxide and its application as a photocatalyst for degradation of aqueous Congo Red
Authors: Priyadarshi Roy Chowdhury
Krishna G Bhattacharyya
Journal: RSC advances (2015)
Discipline: CHEMISTRY
Keywords: Co/Ti layered double hydroxide; semiconductor properties; visible light decolourisation efficiency; photocatalytic efficiency; defect sites
Affiliations: Department of Chemistry, Gauhati University, Guwahati-781014, Assam, India.

Abstract:  2 : 1 Co/Ti layered double hydroxide (LDH) was synthesized hydrothermally using commercially available Co(NO3)2·6H2O and TiCl4, on a urea template. The high surface area material (~180 m2 g-1) had a narrow band gap (2.67 eV) and shallow and deep trap defect sites. The layered nanomaterial exhibited remarkable semiconductor properties and demonstrated excellent visible light decolourisation efficiency for the anionic dye Congo Red in aqueous medium. The photocatalytic efficiency of the LDH was better than common commercial materials in use such as ZnO, ZnS, NiO, CoO, TiO2 and Degussa P25. The presence of different surface states of defect sites in the LDH was confirmed by PL, EIS and XPS measurements. XRD, DRS, FT-IR, AFM, TEM, SEM/EDX and TG/DTG analyses yielded information about the structural, morphological properties and thermal stability of the LDH. BET N2 adsorption-desorption measurements at 77 K gave surface area and porosity data for the LDH. The surface charge characteristics of the LDH were evaluated with ξ-potential measurements over a wide pH-range in aqueous medium. The photocatalytic behaviour towards decolourisation of the dye was evaluated depending on the reaction variables of pH, LDH amount, initial dye concentration and effects of quenchers, and variation of molar ratios of Co/Ti LDH. The pseudo-first order model satisfactorily described the degradation kinetics of the anionic dye. The photocatalytic mechanistic pathways of the LDH were explained on the basis of an electron-hole (e--h+) hopping conduction model and also photosensitization of the dye. The maximum catalytic efficiency was observed with 15.0 mg of LDH at pH 4 for the anionic Congo Red dye at a concentration 1 × 10-5 M. The LDH was stable even after the fifth catalytic cycle, indicating its remarkable efficiency in potential decolourisation treatments. The dye degradation products were analysed with GC-MS and a reaction mechanism was proposed for the breakdown of the dye to simple and less toxic components. 

Retracted: Yes

PubPeer comments:
 Upper right: Figure 10 (C)  TEM image showing layered structure . Notice photocloned margin along its lower edge. Upper left: FIgure 6 (D)  lattice fringe separation exhibited by TEM , from [ Synthesis and characterization of Mn Co Ti LDH and its utilization as a photocatalyst in visible light assisted degradation of aqueous Rhodamine B ] (2016). ![file] Remarkable similarity, after stretching and compression of 6(D). , 
 Figure 10,  (G) AFM micrograph ![file] Contains a repeated section. It also seems to be the source of the  bunny motif and the  duck motif which feature in an **earlier** AFM micrograph [from the same authors, for a different material (Mn Co Ti LDM)] . ![] , 
 The u201c2 : 1 Co Ti LDH spectrumu201d in this paper: ![file] It looks completely similar to the u201c2 : 1 Ni Ti LDH spectrumu201d in another paper by the authors: https: pubpeer.com publications E819499DAFA7443A85150777AA3AFF https: pubs.rsc.org en Content ArticleLanding 2015 DT C5DT00257E ![file] At the very least, the fact that the spectra were already published should have been acknowledged in the figure caption, I suppose. , 
 Retraction notice t[06 Apr 2020.] The Royal Society of Chemistry hereby wholly retracts this RSC Advances article due to concerns with the reliability of the data in the published article. The XPS data in Fig. 4B, E and F have been duplicated in another publication, but reported as a different material.1 A repeating segment can be observed in the TEM image presented in Fig. 10C, which indicates that this image has been manipulated. There are unexpected similarities in the baseline of the EDX spectrum in Fig. 10F and the EDX spectra in other publications, which have all been reported as different materials.1u20133 There are repeating motifs within the AFM image in Fig. 10G, which indicates that this image has been manipulated. Many of these motifs can also be observed in an AFM image in another publication, but representing a different material.2 The image in Fig. 10I is unreliable as it has subsequently been reused in unpublished material to represent different materials. The FTIR data presented in Fig. 16B (blue, red and green spectra) illustrate duplication of data, given that these experiments were reported under different reaction conditions. Given the number and significance of the concerns about the validity of the data, the findings presented in this paper are no longer reliable. Priyadarshi Roy Chowdhury and Krishna G. Bhattacharyya were informed about the retraction of the article but did not respond. Signed: Laura Fisher, Executive Editor, RSC Advances ,