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In the application of various magnetic materials for water treatment, control of surface resistance to acid and alkali corrosion remains largely overlooked, which could greatly extend their service life. We herein prepare amino grafted magnetic graphene oxide composites using a simple one-step cross-link reaction between the graphene oxide and magnetic Fe3O4/C nanoparticles. The as-prepared magnetic graphene oxide composites have long-term stability under acid and alkali solutions and shows an excellent performance in removing Ho(III), a representative rare earth element (REE) from water. The observed adsorption capacity of 72.1 mg Ho(III)/g exceeded that of most magnetic materials previously reported. Regeneration of the magnetic composites was realized in acid and alkali solutions but their structural integrity and physicochemical properties retained even after 18 adsorption-desorption cycles. The current adsorbent also shows excellent adsorption performance for other heavy REEs, such as Er(III), Eu(III), Lu(III), Tm(III), Y(III) and Yb(III). This work can provide a new strategy for constructing an acid and base resistance magnetic graphene oxide for the high-efficient recovery of heavy REEs from aqueous solution.

The adsorbents with high adsorption capacity for simultaneously removing Cr(VI) and Hg(II) from aqueous solutions under broad working pH range are highly desirable but still extremely scarce. Here, a novel adsorbent with multidentate ligands was facilely fabricated by covalently bonding 4-amino-3-hydrazino-5-mercapto- 1,2,4-triazole on graphene oxide via the Schiff’s base reaction. The maximum adsorption capacities of Cr(VI) and Hg(II) on the current adsorbent were 734.2 and 1091.1 mg/g, which were 14.36 and 5.61 times higher than that of the pure graphene oxide, respectively, exceeding those of most adsorbents previously reported. More interestingly, Cr(VI) and Hg(II) concentrations were decreased from 2 mg/L to 0.0001 mg/L for Hg(II) and 0.004 mg/L for Cr(VI), far below the WHO recommended threshold for drinking water. Moreover, the adsorbent shows an excellent performance for simultaneous removal of Cr(VI) and Hg(II) with more than 99.9% and 98.6% removal efficiencies in aqueous solutions. Finally, the adsorbent was successfully applied in dealing with the real industrial effluent, implying huge potential in industrial application. This work offers a new possibility for the removal of the metallic contaminants by rational designing target groups and ligands.

We herein report a facile strategy to prepare poly(allylamine hydrochloride) cross-linked amino-modified graphene oxide (PAH−ASGO) by Schiff-base reactions. The resulting PAH-ASGO exhibited a maximum adsorption capacity of 373.1 mg/g for Cr(VI), which was nearly 9 times higher than that of pure graphene oxide, exceeding that of most GO-based materials previously reported. More significantly, PAH-ASGO can effectively diminish the Cr(VI) concentration from 9.9 mg/L to the extremely low level of 0.004 mg/L within 10 s, far below the maximum allowable level of Cr(VI) (0.05 mg/L) in drinking water. In addition, the adsorbents still displayed excellent removal efficiency of 91.8% after 10 cycles. Considering the broad diversity, we developed also a magnetic PAH−ASGO/Fe3O4 adsorbent by a simple cross-linking reaction to achieve rapid separation of PAH−ASGO from their aqueous solution. Finally, the PAH−ASGO was successfully utilized to treat the actual industrial effluent.

Cr(VI) pollution in wastewater has increasingly become a global environmental problem owing to its acute toxicity. Herein, we present the one-pot procedure for preparing the amino-functionalized (-NH2) graphene oxide (GO-) supported networked Pd–Ag nanowires by co-reduction growth in polyol solution, which show the highly efficient catalytic performance with the excellent cycling stability for the catalytic Cr(VI) reduction by formic acid as an in-situ source of hydrogen at room temperature. The electron transfer from Ag and amino to Pd increases the electron density of Pd, which enhances the catalytic formic acid decomposition and subsequent the catalytic Cr(VI) reduction. The catalytic reduction rate constant of Pd3Ag1/GO-NH2 is determined to be 0.0768 min−1, which is much superior to the monometallic Pd/GO-NH2 and Pd3Ag1/GO. This study provides a novel strategy to develop catalysts for the catalytic reduction of Cr(VI) to Cr(III) in the industrial effluent using formic acid as an in-situ source of hydrogen.

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.