The controlled synthesis and DFT investigation of novel (0D)–(3D) ZnS/SiO2 heterostructures for photocatalytic applications
Authors: M F Abdel Messih
Mohamed F Sanad
M A Ahmed
Ahmed Esmail Shalan
Journal: RSC Advances (2021)
Discipline: CHEMISTRY
Keywords: ZnS/SiO2 photocatalyst; nanocomposites; photodegradation; organic dyes; UV irradiation
Affiliations: Chemistry Department, Central Metallurgical Research and Development Institute (CMRDI)

Abstract:  A ZnS/SiO2 photocatalyst was synthesized using a low-cost sol-gel wet chemical procedure. The as-synthesized ZnS/SiO2 nanocomposites with different molar ratios exhibited superior performance in the photodegradation of two organic dyes under UV irradiation, with complete degradation of both dyes after 2 hours of exposure to UV irradiation. The photocatalyst structure, microstructure, and surface area were studied using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), and nitrogen adsorption (S BET) studies. The results demonstrate that the ZnS/SiO2 photocatalyst with 15% ZnS content has a bandgap energy similar to that of ZnS alone with a higher surface area of approximately 150 m2 g-1, which effectively increases the number of active sites and improves the photocatalytic activity of the prepared material. The measured bandgap energies were compared with the theoretical values obtained using the density functional theory (DFT) method, and the values were found to be very similar, with a low error percentage. In the case of a high ZnS content (greater than 15%), active site blocking occurred, and the removal rate dropped below 50%. The obtained results indicate that the photocatalytic data are in good agreement with the experimental characterization results for the prepared materials, including the BET and XRD results, confirming a close association between the photocatalytic activity and the surface area of the fabricated photocatalyst. 

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PubPeer comments:
 In that paper it is said :  The diffraction peaks of Ni-CoCH CC appear at 17.5u00b0, 33.8u00b0, 35.5u00b0, 39.5u00b0 and 47.3u00b0, which can be well indexed to the typical (0 2 0), (2 2 1), (0 4 0), (2 3 1) and (3 4 0) lattice planes of Co(CO3)0.5(OH)) (JCPDS No. 48-0083), respectively [40]. It reveals that the crystal structure of Ni-CoCH is almost identical to that of Co(CO3)0.5(OH), indicating that partial replacement of nickel ions does not change the crystal structure of Co carbonate hydroxide [29]. The problem is that the lattice planes here are those given in the JCPDS card 48-0083. It has been demonstrated two years ago that the chemical formula in that JCPDS card 48-0083 is considerably wrong and the crystal structure was solved in an hexagonal cell instead of orthorhombic (i.e. the previous indexing was false and no crystal structure was known) : http: scripts.iucr.org cgi-bin paper?S2053229618017734  A quarter of a century after its synthesis and with 200 papers based on its use, `Co(CO3)0.5(OH)u00b70.11H2Ou2032 proves to be Co6(CO3)2(OH)8u00b7H2O from synchrotron powder diffraction data  The successful attempt to solve the crystal structure of Co(CO3)0.5(OH)u00b70.11H2O (denoted CCH), based on synchrotron powder diffraction data, leads to a drastic revision of the chemical formula to Co6(CO3)2(OH)8u00b7H2O [hexau00adcobalt(II) bisu00ad(carbonate) octau00adhydroxide monohydrate] and to a hexau00adgonal cell instead of the orthou00adrhomu00adbic cell suggested previously [Porta et al. (1992). J. Chem. Soc. Faraday Trans. 88, 311u2013319]. This results in a new structure-type related to malachite involving infinite chains of [CoO6] octau00adhedra sharing edges along a short c axis, delimiting tunnels having a three-branched star section. All reports discussing cobalt hyu00addroxyu00adcarbonates (CCH) without any structural knowledge and especially its topotactic decomposition into Co3O4 have, as a result, to be reconsidered. ![file] , 
 Thanks for your valuable advice. According to the literature, the correct chemical formula for the crystal structure of Co(CO3)0.5(OH)u22190.11H2O based on synchrotron powder diffraction data is Co6(CO3)2(OH)8u2219H2O [hexacobalt(II) bis(carbonate) octahydroxide monohydrate] [1]. We have revised the false chemical formula (Co(CO3)0.5(OH)u22190.11H2O) in the JCPDS card 48-0083. The revised version is as follows: The diffraction peaks of Ni-CoCH CC appear at 17.5o, 33.8o, 35.5o, 39.5o and 47.3o, which can be well indexed to the typical (020), (221), (040), (231) and (340) lattice planes of Co6(CO3)2(OH)8u2219H2O (JCPDS No. 48-0083), respectively. It reveals that the crystal structure of Ni-CoCH is almost identical to that of Co6(CO3)2(OH)8u2219H2O, indicating that partial replacement of nickel ions does not change the crystal structure of Co carbonate hydroxide. In this work, Ni-CoCH was prepared via a hydrothermal method. In a typical hydrothermal synthesis, the CO32- and OH- anions which were released from the hydrolysis of urea, interacted with the metal cations (Co2+ and Ni2+) in the aqueous solution to form Ni-CoCH nanoneedles on the surface of carbon cloth backbone. It is known that the phase of Ni-CoCH can be affected by the preparation conditions, such as the types of precipitant and the amount of precipitant. It is also doubtful that the chemical formula of cobalt carbonate hydroxide hydrate in the JCPDS card 48-0083 was still expressed as Co(CO3)0.5(OH)u22190.11H2O in several recently reported works [2-5]. We believe that relative works should be revised according to Ref. 1. References [1] P. Bhojane, A.L. Bail, P.M. Shirage, A quarter of a century after its synthesis and with 200 papers based on its use, u2018Co(CO3)0.5(OH)u22190.11H2Ou2019 proves to be Co6(CO3)2(OH)8u2219H2O from synchrotron powder diffraction data, Acta Crystallorg. C, 75 (2019) 61u201364. [2] G. Zhang, P. Qin, R. Nasser, S. Li, P. Chen, J. Song, Synthesis of Co(CO3)0.5(OH) Ni2(CO3)(OH)2 nanobelts and their application in flexible all-solid-state asymmetric supercapacitor, Chemical Engineering Journal 387 (2020) 124029. [3] B. He, H. Liu, Z. Lin, L. Yan, J. Ning, Y. Zhong, C. Zheng, Z. Zhang, Y. Hu, A new photocatalyst based on Co(CO3)0.5(OH)u22190.11H2O Bi2WO6 nanocomposites for high-efficiency cocatalyst-free O2 evolution, Chemical Engineering Journal 359 (2019) 924u2013932. [4] Y. Liu, X. Cao, L. Cui, Y. Zhong, R. Zheng, D. Wei, C. Barrow, J.M. Razal, W. Yang, J. Liu, Znu2013Niu2013Co trimetallic carbonate hydroxide nanothorns branched on Cu(OH)2 nanorods array based on Cu foam for high-performance asymmetric supercapacitors, J. Power Sources 437 (2019) 226897. [5] H. Gu, Q. Zhong, Y. Zeng, S. Zhang, Y. Bu, Ni and Zn co-substituted Co(CO3)0.5OH self-assembled flowers array for asymmetric supercapacitors, J. Colloid Interf. Sci. 573 (2020) 299u2013306. ,