Adsorption of 3d‐elements onto zinc oxalate dihydrate in aqueous oxalate solutions

Abstract

A study of the sorption of 3d-transition elements onto ZnC 2 O 4 .2H 2 O has been carried out.To reveal the mechanism of the process, the experiments were performed in two media of different oxalate ion concentrations -1.10 -2 and 4.10 -4 mol/l, by the separate and by the joint presence of the microcomponents in the system. In the latter case, copper was also added, the sorption of which has been previously well studied. Different mechanisms of sorption in the different media were found, the determining role of the neutral oxalate complexes having been manifested. In the case of manganese and cobalt, in the medium with oxalate ions deficit, sorption by neutral complexes in the adsorption layer A is supplemented by ion-exchange sorption in the first surface layer S. The sorption of nickel under oxalate ion excess is proved to be an irreversible process, and the concept of its sorption by a mixed complex with the participation of the macrocomponent, Zn[Ni(C 2 O 4 ) 2 ], is advanced. The experimental data show the occurrence of segregation of Mn and Ni by their sorption onto the growth steps, and the absence of segregation of Co by its sorption. An interesting result is the extension of the validity of the Paneth-Fajans rule in the case of so-called complex oxalates, growing by neutral oxalate complexes, such as the oxalates of the macro-and microcompoments, studied in the present work.

Few‐Layered MoxW1−xS2‐Modified CdS Photocatalyst: One‐Step Synthesis with Bifunctional Precursors and Improved H2‐Evolution Activity

“…Subsequently, with the introduction of Cd(OAc) 2 solution, the free S 2− ions immediately react with the foreign Cd 2+ ions to generate CdS nanocrystals considering its fairly small solubility product constant of 8 × 10 −27 (Figure 1A‐c′ and Equation (3) in Figure 1B), which displays distinct Tyndall effect in the photograph of Figure 1C‐c. Simultaneously, according to the Fajans rule, [ 50–52 ] the free ions (MoS 4 2− and WS 4 2− ) in the mixed solution are instantly anchored on CdS surface to construct the colloidal MoS 4 2− ‐WS 4 2− /CdS nanocrystals (Figure 1A‐c and Equation (4) in Figure 1B). During the succedent solvothermal process, the adsorbed MoS 4 2− and WS 4 2− ions on CdS surface can in‐situ transform into few‐layered Mo x W 1− x S 2 nanosheets to produce the few‐layered Mo x W 1− x S 2 ‐modified CdS photocatalyst (Figure 1A‐d and Equation (5) in Figure 1B), which can be well confirmed by the following color change of samples.…”

Homojunction CdS Photocatalysts with a Massive S2–-Adsorbed Surface Phase: One-Step Facile Synthesis and High H2-Evolution Performance

“…Second, a certain amount of Cd 2+ solution is dropped quickly into the above h -CdS suspension under continuous stirring. In this case, owning to the ionic adsorption of the Fajans rule, − the Cd 2+ ions can be steadily and homogeneously adsorbed on the h -CdS surface to produce Cd 2+ -adsorbed h -CdS particles (Figure B­(f)). Meanwhile, its corresponding optical picture (Figure C­(f 1 )) displays h -CdS powdered precipitate, similar to that of Figure C­(e 1 ).…”

Suspensible Cubic-Phase CdS Nanocrystal Photocatalyst: Facile Synthesis and Highly Efficient H2-Evolution Performance in a Sulfur-Rich System

“…Owing to the rapid and complete consumption of Cd 2+ ions, the produced CdS nanocrystals can be closely surrounded by the excessive S 2– /SO 3 2– ions. According to the Fajans rule for ionic adsorption (namely, the ions that form the compound will be adsorbed preferentially when two or more types of ions are available for adsorption), − the excessive S 2– ions can be easily and preferentially adsorbed on the c -CdS-NC surface (Figure A), resulting in the formation of cottony and suspensible CdS photocatalysts (shown in the photograph). According to its XRD and TEM results (Figure A–C), the suspensible nanocrystals can be attributed to cubic-phase CdS (JCPDS Card No.…”