Selective recovery of Au(III) from acidic electronic-waste (e-waste) leachates remains challenging because abundant competing metal ions can interfere with gold capture. Here, a nitrogen-rich triazine-based porous aromatic framework (triazine-PAF) was developed for selective Au(III) recovery through coordinated adsorption and reduction. Triazine-PAF exhibited an experimental Au(III) uptake of 2289.86 mg g−1, with a Langmuir-predicted maximum capacity of 2525 mg g−1, together with rapid adsorption kinetics and high selectivity toward Au(III) over competing metal ions. XPS, XRD, and density functional theory analyses indicate that Au(III) capture involves strong interactions with nitrogen coordination sites accompanied by partial reduction to lower-valent Au species and metallic Au(0). The Au/N molar ratio of 1.80 exceeds the contribution expected from simple 1:1 N–Au coordination, suggesting that reduction-mediated regeneration of coordination sites contributes to the high Au uptake. In real acidic CPU leachate containing a > 150-fold excess of Cu(II), triazine-PAF selectively recovered 86.44% of Au(III) while exhibiting negligible co-adsorption of major base metals. The adsorbent retained approximately 86% of its initial capacity after five regeneration cycles. These results demonstrate a porous nitrogen-rich platform for selective gold recovery and resource valorization from complex e-waste leachates.
Cadmium sulfide (CdS) quantum dots (QDs) were grown in situ on graphene nanosheets (GNS) through a thiol-capped aqueous route (CdCl2/Na2S with thioglycolic acid as the capping ligand), using GNS obtained by glucose-assisted hydrothermal reduction of graphene oxide (GO) prepared by a modified Hummers method. X-ray diffraction (XRD) showed the contraction of the interlayer spacing from 0.81 nm (GO) to ∼0.34 nm (GNS) and the formation of cubic CdS with a Scherrer crystallite size of ∼3.5 nm. Transmission electron microscopy revealed nearly spherical CdS QDs (mean diameter ∼3.5 nm) dispersed on the GNS, with lattice fringes of 0.32 and 0.21 nm assigned to the (111) and (220) planes of cubic CdS. Raman spectroscopy (ID/IG = 1.20 for GNS and 1.24 for CdS–GNS) indicated that the sp2 carbon framework was largely preserved after QD decoration, and X-ray photoelectron spectroscopy confirmed Cd2+ (Cd 3d5/2, 405.1 eV) and S2− (S 2p3/2, 161.5 eV) chemical states. Photoluminescence quenching, a ∼ 4-fold lower charge-transfer resistance in electrochemical impedance spectroscopy (0.78 vs. 3.22 kΩ) and an anodic shift of the flat-band potential in Mott–Schottky analysis (−0.89 → −0.52 V vs. RHE) together evidence efficient electron transfer from CdS to the GNS. The composite exhibited an optical band gap of ∼2.80 eV, and Mott–Schottky analysis placed the conduction- and valence-band edges of the CdS QDs at ≈ −0.99 and +1.81 V vs. RHE (Mulliken estimate: −0.72 and +2.08 V), confirming that O2 reduction by photogenerated electrons is thermodynamically allowed. Under visible-light (white LED) irradiation, CdS–GNS removed 94.9% of Rhodamine B (RhB) in 120 min after a 60 min dark equilibration, compared with 82.4% for pristine CdS QDs; the pseudo-first-order rate constant increased from 1.27 × 10−2 to 2.03 × 10−2 min−1. Dark adsorption accounted for 42.1% and 11.9% RhB removal on CdS–GNS and CdS QDs, respectively, showing that the GNS support enhances both dye pre-concentration and charge separation. Scavenger tests (inhibition order EDTA > IPA > DMSO, with no inhibition by ascorbic acid) identified photogenerated holes as the dominant oxidizing species, with a secondary contribution from hydroxyl radicals. CdS–GNS retained ∼85% of its initial RhB removal efficiency after five successive photocatalytic cycles, indicating reasonable reusability.
To protect the surfaces of aluminum and its alloys from corrosion, mononuclear trimethylacetate zinc(II) complexes with 2,2′-dipyridyl, 4,4′-dimethyl-, 4,4′-dinonyl-2,2′-dipyridyl [ZnL(piv)2] and [ZnL(piv)2(H2O)] (L = bpy, Me2bpy, Nn2bpy) were synthesized and fully characterized by monocrystal X-Ray and PXRD. When heated in Ar, the onset temperature of decomposition of the complex increases for L in the row bpy-Me2bpy-Nn2bpy, complexes with bpy and Me2bpy melt after the onset of decomposition, with Nn2bpy – before. Simple method of the AA-6063 alloy surface protection was found: self-assembly of protective coatings on the surface by maintaining a metal plate in an EtOH solution of complexes [ZnL(piv)2(H2O)] was carried out. In the case of treatment with [Zn(Nn2bpy)(piv)2(H2O)] complex, superhydrophobization of the surface occurs, whereas for the bpy, Me2bpy compounds – not. The alloy surface with protective coating was studied by SEM, EDS, XPS, and the presence of Zn2+ complex fragments on it was approved. The protective capacity of the coatings increases for complexes with L in the row bpy-Me2bpy-Nn2bpy according to the data of polarization measurements, electrochemical impedance spectroscopy, and corrosion tests in a salt spray chamber. In addition, theoretical modeling of the adsorption of [ZnL(piv)2] onto the aluminum surface was performed within the framework of DFT. Increasing in the total adsorption energy takes place for complexes with L in the same row bpy-Me2bpy-Nn2bpy. The most significant change in the geometry of the modeled adsorbed complexes and significant contribution of the energy of non-covalent interactions is observed for compounds with substituted bipyridines. The role of non-covalent interactions in the adsorption efficiency is discussed.
This work reports the one-pot synthesis of three closely related Pd(II) thiosemicarbazone complexes, [Pd(L1)(PPh3)DMSO], [Pd(L1)(PPh3)DMF], and [Pd(L2)(PPh3)], where HL1 = 2-hydroxy-1-naphthaldehyde thiosemicarbazone and HL2 = 2-hydroxy-1-naphthaldehyde-N(4)-methylthiosemicarbazone. A systematic comparative investigation was undertaken to elucidate how subtle ligand modification and lattice-solvent incorporation modulate the molecular structures, supramolecular assembly, and interaction energetics of these complexes. Single-crystal X-ray diffraction revealed that one complex crystallizes in unsolvated, DMF-solvated, and DMSO-solvated forms, exhibiting similar square-planar coordination geometries but markedly different supramolecular architectures. Solvent inclusion reorganizes the unsolvated packing into distinct solvent-mediated architectures, whereas methyl substitution promotes a more compact columnar arrangement dominated by C–H···C(π) interactions. Hirshfeld surface and two-dimensional fingerprint plot analyses demonstrate that lattice solvents substantially modify the intermolecular contact distribution, primarily through the introduction of strong N–H···O hydrogen bonds and attenuation of π···π stacking interactions. Density functional theory calculations of representative molecular dimers further show that DMSO engages in a more diverse network of stabilizing interactions than DMF, while the most stable dimer of methyl-substituted complex is reinforced by cooperative N–H···C(π), C–H···C(π), and C–H···S interactions. QTAIM analysis confirms the closed-shell nature of the intermolecular contacts and provides quantitative estimates of their individual interaction strengths. Experimental UV–Vis spectra, supported by TD-DFT calculations, indicate that methyl substitution has only a minor influence on the electronic structure and optical absorption properties, with the lowest-energy transitions arising predominantly from HOMO→LUMO and HOMO→LUMO+1 excitations. Overall, lattice solvent inclusion emerges as the principal factor governing supramolecular organization and intermolecular interaction patterns, whereas methyl substitution exerts a comparatively limited effect on the electronic and optical properties.
Photocatalytic reduction of hexavalent chromium (Cr(VI)) to the less toxic trivalent form (Cr(III)) offers a promising route for heavy metal wastewater remediation. Herein, we report an N,S co-doped carbon nanoflask/TiO2/Zn2In2S5 (NSFTZ) composite synthesized via a three-step strategy coupling hydrothermal, sol–gel, and water-bath methods. NSFTZ exhibits a narrow band gap of 1.73 eV (versus 3.01 eV for TiO2 and 2.40 eV for Zn2In2S5), strong UV–visible light absorption extending to ∼717 nm, and a specific surface area of 120.47 m2/g. Under UV–visible light at pH 5.0, NSFTZ achieved 99.16% Cr(VI) removal within 120 min, with a rate constant (0.03574 min−1) 148.92 and 4.08 times that of pristine TiO2 and Zn2In2S5, respectively. The Langmuir maximum removal capacity reached 1700.66 mg/g at 298 K, and the composite retained over 91% efficiency after seven consecutive cycles. In real electroplating wastewater (55.82 mg/L Cr(VI)), 99.39% removal was attained within 20 min under UV–visible light, reducing residual Cr(VI) to 0.34 mg/L, well below the Chinese industrial discharge limit of 0.5 mg/L. Mechanistically, an S-scheme TiO2/Zn2In2S5 heterojunction, coupled with N,S-ACF as a conductive electron mediator, enables multi-level charge transfer, while photogenerated electrons and superoxide radicals were identified as the dominant active species. Ultimately, this work demonstrates a robust material platform that seamlessly integrates rapid Cr(VI) photoreduction, stable Cr(III) immobilization, and excellent cyclic reusability for practical wastewater remediation.
