Shouwei Zhang

In Situ Ion Exchange Synthesis of Strongly Coupled Ag@AgCl/g-C3N4 Porous Nanosheets as Plasmonic Photocatalyst for Highly Efficient Visible-Light Photocatalysis

A novel efficient Ag@AgCl/g-C3N4 plasmonic photocatalyst was synthesized by a rational in situ ion exchange approach between exfoliated g-C3N4 nanosheets with porous 2D morphology and AgNO3. The as-prepared Ag@AgCl-9/g-C3N4 plasmonic photocatalyst exhibited excellent photocatalytic performance under visible light irradiation for rhodamine B degradation with a rate constant of 0.1954 min(-1), which is ∼41.6 and ∼16.8 times higher than those of the g-C3N4 (∼0.0047 min(-1)) and Ag/AgCl (∼0.0116 min(-1)), respectively. The degradation of methylene blue, methyl orange, and colorless phenol further confirmed the broad spectrum photocatalytic degradation abilities of Ag@AgCl-9/g-C3N4. These results suggested that an integration of the synergetic effect of suitable size plasmonic Ag@AgCl and strong coupling effect between the Ag@AgCl nanoparticles and the exfoliated porous g-C3N4 nanosheets was superior for visible-light-responsive and fast separation of photogenerated electron-hole pairs, thus significantly improving the photocatalytic efficiency. This work may provide a novel concept for the rational design of stable and high performance g-C3N4-based plasmonic photocatalysts for unique photochemical reaction.

In Situ Synthesis of Water-Soluble Magnetic Graphitic Carbon Nitride Photocatalyst and Its Synergistic Catalytic Performance

Water-soluble magnetic-functionalized graphitic carbon nitride (g-C3N4) composites were synthesized successfully by in situ decorating spinel ZnFe2O4 nanoparticles on g-C3N4 sheets (CN-ZnFe) through a one-step solvothermal method. The magnetic properties of CN-ZnFe can be effectively controlled via tuning the coverage density and the size of ZnFe2O4 nanoparticles. The results indicate that the CN-ZnFe exhibits excellent photocatalytic efficiency for methyl orange (MO) and fast separation from aqueous solution by magnet. Interestingly, the catalytic performance of the CN-ZnFe is strongly dependent on the loading of ZnFe2O4. The optimum activity of 160CN-ZnFe photocatalyst is almost 6.4 and 5.6 times higher than those of individual g-C3N4 and ZnFe2O4 toward MO degradation, respectively. By carefully investigating the influence factors, a possible mechanism is proposed and it is believed that the synergistic effect of g-C3N4 and ZnFe2O4, the smaller particle size, and the high solubility in water contribute to the effective electron-hole pairs separation and excellent photocatalytic efficiency. This work could provide new insights that g-C3N4 sheets function as good support to develop highly efficient g-C3N4-based magnetic photocatalysts in environmental pollution cleanup.

Porous magnetic carbon sheets from biomass as an adsorbent for the fast removal of organic pollutants from aqueous solution

A facile and scalable in situ synthetic strategy (simultaneous template–graphitization) was developed to fabricate carbon-stabilized Fe/Fe3C nanoparticles, which were homogeneously embedded in porous carbon sheets (PMCS) as an excellent adsorbent for wastewater treatment. In the synthesis, the graphitic catalyst precursor (Fe(NO3)3) and template agent (Al(NO3)3) were introduced simultaneously into the agar hydrogel through the coordination of the metal precursor with the functional groups of agar, thus resulting in simultaneous realization of the template and graphitization of the carbon source under heat treatment. The PMCS with high surface area (1023.2 m2 g−1) exhibited high adsorption capacities and fast adsorption rates toward dyes. Using methylene blue (MB), methyl orange (MO) and crystal violet (CV) as model pollutants, the maximum adsorption capabilities for MB, MO, and CV reached 1615.9, 1062.4 and 1728.3 mg g−1, respectively. Moreover, the possibility of magnetic separation also facilitated its application in wastewater treatment on a large scale. This multifunctional material can potentially be used as a super adsorbent to efficiently remove pollutants from wastewater.

Rationally designed 1D Ag@AgVO3 nanowire/graphene/protonated g-C3N4 nanosheet heterojunctions for enhanced photocatalysis via electrostatic self-assembly and photochemical reduction methods

1D Ag@AgVO3 nanowire/graphene/protonated g-C3N4 nanosheet (Ag@AgVO3/rGO/PCN) heterojunctions are fabricated via a simple electrostatic self-assembly process followed by a photochemical reduction method. In this hybrid structure, 1D Ag@AgVO3 nanowires penetrate through 2D nanosheets (graphene and PCN), forming a 3D hybrid photocatalyst, which is applied as an efficient visible light driven photocatalyst for organic pollutant degradation. Its enhanced photocatalytic activity is ascribed to the well-known electronic conductivity of 2D graphene, the intense visible light absorption of 1D Ag@AgVO3 nanowires, large surface areas and rapid photogenerated charge interface transfer and separation. Our results provide a facile way to fabricate hierarchical g-C3N4-based photocatalysts in a controlled manner and highlight promising prospects by adopting an integrative 1D and 2D nanomaterial strategy to design more efficient semiconductor-based composite photocatalysts with high photocatalytic activities and a wide spectral response toward environmental and energy applications.

Polyaniline nanorods dotted on graphene oxide nanosheets as a novel super adsorbent for Cr(VI)

Hierarchical nanocomposites of polyaniline (PANI) nanorods array on graphene oxide (GO) nanosheets are successfully obtained by dilute polymerization under -20 °C. They exhibit excellent water treatment performance with a superb removal capacity of 1149.4 mg g(-1) for Cr(VI).

Superior adsorption capacity of hierarchical iron oxide@magnesium silicate magnetic nanorods for fast removal of organic pollutants from aqueous solution

Novel hierarchical core–shell iron oxide@magnesium silicate magnetic nanorods (HIO@MgSi) were fabricated via a versatile sol–gel process through hydrothermal reaction. They contain magnetic iron oxide (Fe3O4) cores and hierarchical shells (MgSi) made of ultrathin nanosheets (ca. 5 nm). Using methylene blue as a model compound, the HIO@MgSi nanorods showed fast adsorption kinetics and a superb adsorption capacity. 99.3% of methylene blue was adsorbed onto the surface of the HIO@MgSi nanorods in 40 min contact time. A maximum adsorption capacity of 2020.20 mg g−1 was achieved after 4 h. This study indicated that HIO@MgSi nanorods can be used as a potential super adsorbent to remove cationic organic pollutants effectively and rapidly from large volumes of industrial wastewater or drinking water.

Formation of Fe3O4@MnO2 ball-in-ball hollow spheres as a high performance catalyst with enhanced catalytic performances

While the synthesis of heterogeneous catalysts is well established, it is extremely challenging to fabricate complex hollow structures with mixed transition metal oxides. Herein, we report a facile in situ growth process of SiO2@Fe3O4@MnO2, followed by an etching method to synthesize a hierarchical hollow structure, namely Fe3O4@MnO2 ball-in-ball hollow spheres (Fe3O4@MnO2 BBHs). The as-prepared Fe3O4@MnO2 BBHs were applied to degrade methylene blue (MB) by catalytic generation of active radicals from peroxymonosulfate (PMS), exhibiting the merits of excellent catalytic performance, easy separation, good stability and recyclability. In this architecture, the degradation process can be divided into three layers. The outer hierarchical MnO2 nanosheets could accumulate and transport the pollutants by electrostatic interactions and catalyze the generation of active radicals for degradation. Both the inner MnO2 nanosheets and the outer Fe3O4 hollows could produce active radicals to accelerate the pollutant degradation. The active catalytic sites also existed in the inner Fe3O4 hollows, which could further degrade the highly concentrated pollutants in the hollows. This work provides new strategies for the controllable synthesis of complex hollow structures and their application in environmental remediation.

Efficient enrichment of uranium(VI) on amidoximated magnetite/graphene oxide composites

Amidoximated magnetite/graphene oxide (AOMGO) composites were synthesized and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transformed infrared (FTIR) spectroscopy. The synthesized AOMGO composites were applied to adsorb uranium(VI) from aqueous solutions and could be easily separated by an external magnetic field. The kinetic process of U(VI) sorption on AOMGO composites reached equilibrium within 2 h. Effects of pH, ionic strength and coexisted ions on the sorption of U(VI) on AOMGO composites were investigated. The results indicated that U(VI) sorption on AOMGO composites was strongly dependent on pH and independent of ionic strength. The sorption isotherm agreed well with the Langmuir model, having a maximum sorption capacity of 1.197 mmol g−1 at pH = 5.0 ± 0.1 and T = 298 K. Thermodynamic parameters calculated from the temperature-dependent sorption isotherms suggested that the sorption of U(VI) on AOMGO composites was an endothermic and spontaneous process. The fast and efficient sorption performance suggests that AOMGO composites are potential and suitable candidates for the preconcentration and separation of U(VI) from contaminated wastewater and seawater.

Amidoxime-functionalized magnetic mesoporous silica for selective sorption of U(VI)

Amidoxime-functionalized magnetic mesoporous silica (MMS-AO) microspheres were synthesized through co-condensation of tetraethyl orthosilicate (TEOS) and 2-cyanoethyltriethoxysilane (CTES) on the surface of silica-coated Fe3O4 followed by chemical modification of nitrile into amidoxime. The synthesized microspheres exhibit a typical sandwich structure with an inner core of Fe3O4, a middle layer of nonporous silica and an outer layer of amidoxime-functionalized mesoporous silica. Owing to the mesoporous structure and amidoxime functionalization, sorption of U(VI) by MMS-AO reaches equilibrium in 2 h of contact time with a maximum sorption capacity of 1.165 mmol g−1 (277.3 mg g−1) at pH = 5.0 ± 0.1 and T = 298 K, which is much higher than the results previously reported for other magnetic materials. The sorption process is strongly dependent on pH but independent of ionic strength, indicating that the predominant sorption mechanism is inner-sphere surface complexation. The selectivity of MMS-AO for U(VI) is remarkably improved in comparison with that of magnetic mesoporous silica without amidoxime functionalization. U(VI)-loaded MMS-AO can be conveniently separated from aqueous solutions with an external magnetic field and efficiently regenerated using 1 mol L−1 HCl with only a small decrease in U(VI) sorption capacity. These results suggest that MMS-AO shows promise as a future candidate for selective separation of U(VI) from aqueous solutions in possible real applications.

Hybrid 0D–2D Nanoheterostructures: In Situ Growth of Amorphous Silver Silicates Dots on g-C3N4 Nanosheets for Full-Spectrum Photocatalysis

The smaller particle sizes, better dispersion, and more heterojunction interfaces can enhance the photocatalytic performance of photocatalysts. Herein, ultradispersed amorphous silver silicates/ultrathin g-C3N4 nanosheets heterojunction composites (a-AgSiO/CNNS) with intimate interfacial coupling effect were synthesized through the facile in situ precipitation of ultrafine a-AgSiO (∼5.2 nm) uniformly dispersed on the entire surface of hierarchical ultrathin CNNS. In this process, the ultrathin CNNS not only perform as the support to form heterostructures but also are employed as dispersant to confine the aggregation of a-AgSiO nanoparticles. Notably, the optimum photocatalytic activity of a-AgSiO/CNNS-500 composite is ∼36 and 13 times higher than that of CNNS toward the degradation of rhodamine B and tetracycline, respectively. The excellent photocatalytic activity can be attributed to the synergistic interactions of heterojunction with strong interfacial coupling effect, improved visible light absorbance, abundant heterojunction interfaces, and fully exposed reactive sites, which originate from the well-defined nanostructures such as uniform packing of the ultrasmall a-AgSiO, the intimate and maximum coupling interfaces between a-AgSiO and CNNS. We believe that such an easy and scalable synthetic strategy can be further extended to the fabrication of other ultrafine semiconductors coupled with g-C3N4 for increasing its photocatalytic performance.