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The pollutant of hexavalent chromium (Cr(VI)) threats to the environment as well as to the human beings due to its strong toxicity, carcinogenicity, mobility and undegradability. Herein, a novel porous aminated red phosphorus (RP) nanosheet photocatalyst was synthesized to remove Cr(VI) from water through adsorption and in-situ photocatalytic reduction. The introduction of NH2 on the surface of RP nanosheet could effectively improve adsorption and photocatalytic reduction performance for Cr(VI) removal during visible light irradiation. As a result, the optimized RP-AP-0.5 (AP: 3-aminopropyltriethoxysilane) nanosheet displays the apparent reaction rate constant of 0.0190 min−1, which is 5.5 times higher than that of pure RP (0.0035 min−1), the 96.5% reduction efficiency for Cr(VI) within 120 min at pH = 4.8 ± 0.1 and still exhibits more than 95% removal efficiency after 5 cycles at the same condition. The enhanced Cr(VI) removal performance of the aminated RP nanosheet can be assigned to accelerating the interfacial reaction dynamics and more effective electron-hole separation owing to the presence of NH2 groups. This study provides a new method to develop high-efficiency metal-free photocatalysts with NH2 modification for Cr(VI) removal.

It is highly desirable but remains extremely challenging to develop a facile strategy to prepare adsorbent for dealing with heavy metal pollution in water. Here, we report a facile approach for preparing sulfydryl-functionalized graphene oxide (S-GO) by cross-linking method with an unprecedented adsorption capacity and ultrahigh selectivity for efficient Hg(II) removal. The adsorbents exhibit a prominent performance in capturing Hg(II) from wastewater with a record-high adsorption capacity of 3490 mg/g and rapid kinetics to reduce Hg(II) contaminants below the discharge standard of drinking water (2 ppb) within 60 min under a wide pH range even in the coexistent of other interfering metal ions. In addition, the adsorbents can be also easily recycled and reused multiple times with no apparent decline in removal efficiency. Considering the broad diversity, we developed also a magnetic Fe3O4/S-GO adsorbent by a simple chemical cross-linking reaction to achieve rapid separation of S-GO from their aqueous solution. In addition, the adsorbents were successfully applied in dealing with the practical industrial wastewater. The results indicate the potential of rationally designed sulfydryl-functionalized graphene oxide for high performance Hg(II) removal.

We herein developed a facile method to prepare PEI grafted amino-functionalized graphene oxide nanosheets, which exhibit a high selectivity in capturing Cr(VI) contaminants from aqueous solutions with an ultrahigh adsorption capacity of 1185 mg/g and fast kinetics to reduce trace Cr(VI) concentrations below the allowed safe levels for drinking water defined by the WHO (0.05 mg/L) within 15 min in the presence of other coexistent ions. To the best of our knowledge, the adsorption capacity of the composites is highest among all PEI functional adsorbents reported so far. Furthermore, the cycle experiments indicated that the composites still exhibited excellent adsorption performance after 40 cycles. The adsorption-reduction mechanism of Cr(VI) on composites was further confirmed. Moreover, the separation performance of the composites was further improved by introducing magnetic nanoparticles on the surface of the composites. Finally, the composites were successfully utilized in dealing with the actual industrial effluent.

There is an increasingly significant issue on Cr(VI) pollution in chemical industry and environmental protection. In this study, we have successfully synthesized CoS2/g-C3N4-rGO hybrid nanocomposites via a simple one-pot solvothermal method as an effective photocatalyst. The CoS2/g-C3N4 heterostructure on rGO showed improved photocatalytic performance for Cr(VI) reduction during visible light irradiation. The optimized photocatalyst shows the 99.8% reduction efficiency for Cr(VI) within 120 min at pH = 2 and still exhibits more than 98% removal efficiency after 5 cycles at the same condition. The enhanced photocatalytic performance of the hybrid nanocomposites can be assigned to the enhanced utilization of visible light arising from the coupling effect in the hybrid nanocomposites and more effective electron-hole pairs separation in heterostructure junction, and large specific surface area and more exposing active sites of CoS2 dispersed on rGO. This study provides a new method to develop high-efficiency photocatalysts for Cr(VI) removal.

It is extremely desirable but challenging to develop a facile synthesis method to directly prepare reusable and longtime stable magnetic graphene oxide (GO) adsorbent. Here, a new approach to prepare a magnetic GO for removing the heavy metal ions is reported by using n-Propyltrimethoxysilane (NPTS) as a cross-coupling agent to connect Fe3O4/SiO2 and GO. The as-prepared magnetic GO can be separated quickly from their aqueous solution by the permanent magnet and also exhibited excellent adsorption performance for Cd(II) and Pb(II) with maximum adsorption capacities for Cd(II) and Pb(II) to 128.2 and 385.1 mg/g under neutral conditions, respectively. The presence of other ions such as Na(I) and K(I), had little influence on the Cd(II) and Pb(II) removal efficiency. Moreover, the as-prepared Fe3O4/SiO2-GO adsorbents can be recycled and exhibited good reproducibility. Thus, the magnetic GO adsorbents are effective materials for the removal of heavy metal ions and thus could offer a new platform for water cleanup.