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Highlights: Confined space/water in graphene hydrogel was constructed and controlled. Adsorption capacity of porous adsorbents was enhanced by filling confined water. Incomplete hydrogen bonding in confined water contributes to adsorption. Confined water has been proven to be of great importance due to its pervasiveness and contribution to life and many fields of scientific research. However, the control and characterization of confined water are a challenge. Herein, a confined space is constructed by flexibly changing the pH of a graphene oxide dispersion under the self-assembly process of a graphene hydrogel (GH), and the confined space is adjusted with variation from 10.04 to 3.52 nm. Confined water content in GH increases when the pore diameter of the confined space decreases; the corresponding adsorption capacity increases from 243.04 to 442.91 mg g−1. Moreover, attenuated total reflectance Fourier transform infrared spectroscopy and Raman spectroscopy are utilized to analyze the hydrogen bonding structure qualitatively and quantitatively, and correlation analysis reveals that the improvement in the adsorption capacity is caused by incomplete hydrogen bonding in the confined water. Further, confined water is assembled into four typical porous commercial adsorbents, and a remarkable enhancement of the adsorption capacity is achieved. This research demonstrates the application potential for the extraordinary properties of confined water and has implications for the development of highly effective confined water-modified adsorbents. [ABSTRACT FROM AUTHOR]

An efficient and environmentally friendly synthesis method was applied for preparation of graphene hydrogel (GH) adsorbents via one-step hydrothermal reduction. By means of characterizations, the possible assembly mechanism of GH was discussed. The Response surface methodology (RSM) was firstly used to evaluate systematically the interactions of synthesis reduction conditions (i.e. graphene oxide initial concentration, reducer dosage, temperature and reaction time) on GH adsorption capacity of CIP. The affecting degree order of the four factors on the adsorption capacity was obtained, thus provide a guidance for GH adsorbents design. In addition, the adsorption enhancement effect of water in GH was raised. Besides, the multiple ciprofloxacin adsorption mechanisms of GH were also investigated and summarized, indicating GH possesses a promising potential in practical application. This finding indicates that GH may be an efficient adsorbent for antibiotic pollutants removal in water purification. Graphene hydrogel is an efficient adsorbent for antibiotic pollutants removal in water purification. Unlabelled Image • Graphene hydrogel has excellent adsorption properties for ciprofloxacin. • Adsorption enhancement effect of water in graphene hydrogel has been proved • RSM was used to optimize the synthesis condition and adsorption properties. • Graphene hydrogel possesses a promising potential in practical application. [ABSTRACT FROM AUTHOR]

There are huge demands for the development of green, environmentally friendly, and easily prepared cationic adsorbents for treatment of chromium-contaminated water. In this research, we demonstrate the fabrication of a novel polyvinylamine-grafted polypropylene membrane (PPM-PVAm) for Cr(VI) adsorption. Based on a rapid two-step method, polypropylene membrane (PPM) was grafted with high biomedical safety N-vinylformamide (NVF), and then amino groups were generated via hydrolysis of the poly(N-vinylformamide) (PNVF) and these amino groups could be protonated under acidic condition as Cr(VI) adsorbing sites. The effects of both the PNVF grafting rate and its degree of hydrolysis on the adsorption performance of PPM-PVAm were investigated. The membrane with a PNVF grafting rate around 55% (wt) and a degree of hydrolysis around 70–80% exhibits the best performance for Cr(VI) adsorption under the optimal conditions, i.e. pH 2 at about 40 °C. The adsorption of Cr(VI) on PPM-PVAm matches the Langmuir model, showing a maximum Cr(VI) adsorption capacity of 208.3 mg per gram dry membrane. PPM-PVAm could be deprotonated under alkaline condition so the adsorbed Cr(VI) could be easily removed by NaOH/NaCl aqueous solution. The membrane shows excellent recycling performance, and 90.6% of the adsorption capability remains even after 10 cycles of adsorption-desorption test. Combining the unique performance and eco-friendly process in the fabrication of the membrane, PPM-PVAm shows great potential in adsorptive removal of Cr(VI) from water. [Display omitted] • A new polypropylene membrane with polyvinylamine modified (PPM-PVAm) has been easily and rapidly prepared. • NVF as a grafting monomer has low toxicity and high biomedical safety. • PPM-PVAm could be protonated to obtain active sites for Cr(VI) adsorption and deprotonated under different pH condition. • PPM-PVAm membrane showed good adsorption ability of Cr(VI). • The recycling performance of Cr(VI) on PPM-PVAM was explored and this membrane showed excellent recycling performance. [ABSTRACT FROM AUTHOR]

[Display omitted] Eliminating the environmental risks of Hexavalent Chromium (Cr (VI)) in aqueous environment was of great importance. Herein, we developed a flexible one-pot approach to synthesize novel amino-functional graphene sponge adsorbents (AFGS), in which graphene nanosheets assembled into 3D network on melamine sponge skeletons with the assistance of ethylene diamine. Benefiting from the functionalization of amino groups, AFGS showed outstanding adsorption capacity (166.46 mg g−1) because of the strong affinity with Cr (VI). Moreover, AFGS could reduce Cr (VI) into less toxic Cr (III) in low pH. The adsorption-reduction mechanism of Cr (VI) on AFGS was investigated in-depth via L-edge X-ray adsorption spectra and XPS spectra. The excellent mechanical strength, structural stability and cycling performance verified the potential of AFGS adsorbents in treating chromium containing wastewater. [ABSTRACT FROM AUTHOR]

Inorganic-organic composite hydrogels have attracted much attention in recent years. In this study, an amino-functionalized graphene/alginate double-network hydrogel (NH 2 -DN) with excellent mechanical and adsorption properties was successfully prepared. Triethylenetetramine (TETA) was used as a crosslinker which promotes random few-layer graphene sheets stacking and resulted in a reduced graphene oxide (rGO) network, containing mesopore and macropore structures on the hydrogel surface. Compared to single network hydrogel, enhanced thermal stability and mechanical properties were achieved in NH 2 -DN. The elasticity modulus was improved by approximately 3 times due to the formation of the double-network. More importantly, NH 2 -DN exhibited excellent adsorption properties for typical emerging contaminants (Cu2+ and ciprofloxacin (CIP)). Compared with that of an ordinary graphene/alginate single-network hydrogel (SN), the adsorption capacity of the NH 2 -DN for Cu2+ and CIP reached 153.91 mg g−1 and 301.36 mg g−1, respectively, which was increased by 130% and 182%, respectively. Adsorption isotherm and kinetic analyses reveal that the adsorption process of CIP onto the NH 2 -DN was dominated by chemical affinity. Adsorption properties were comprehensively examined, including the effects of the solid-liquid ratios, pH, and ionic strength. NH 2 -DN retained 94% of its adsorption capacity when the ionic strength was 0.5 mol L−1 and maintained at least 87% of its adsorption capacity in weak acidic and alkaline solutions. This novel amino-functionalized organic-inorganic hydrogel has great potential in environmental applications owing to its outstanding physicochemical, mechanical, and adsorption properties for emerging contaminants in wastewater. The novel amino functionalized graphene/Alginate double network hydrogel could be potentially applied in the removal of emerging contaminates in wastewater by π–π EDA interaction, hydrogen bonding and electrostatic interaction, owing to its outstanding physicochemical, mechanical and adsorption properties. Image 1 • Amino-functionalized graphene/alginate double-network hydrogel was prepared. • Mechanical strength and thermal stability of NH 2 -DN was significantly improved. • NH 2 -DN exhibited excellent adsorption property (Cu2+: 153.91, CIP: 301.36 mg/g). [ABSTRACT FROM AUTHOR]

Novel polysaccharide-based sodium alginate/ĸ-carrageenan double-network gel beads were prepared via a facile ionically cross-linking method with low-swelling, enhanced mechanical properties, and excellent adsorption performance. • Sodium alginate/ĸ-carrageenan double-network gel beads were prepared. • SK exhibited enhanced mechanical property (elastic modulus 1.3 Mpa). • SK exhibited excellent adsorption property for CIP (245.1 mg/g). • SK have a reduced swelling property compared to a single ĸ-CG/Ca2+ network. Double-network gel is composed of two kinds of crosslinked organic/inorganic networks, which has a good prospect of environmental application and its application in the antibiotic removal has important practical significance. Novel polysaccharide-based double-network gel bead (SK) with low-swelling, enhanced mechanical properties and excellent adsorption capacity of ciprofloxacin hydrochloride (CIP) was prepared via a facile ionically cross-linking method. Mechanical properties tests and swelling experiments showed that the sorbent has an enhanced mechanical property with stress of 1.07 MPa and an elastic modulus of 1.3 MPa at 90% strain and a reduced swelling property compared to a single ĸ-CG/Ca2+ network. The adsorption performances of SK gel for CIP were investigated by changing the ratio of raw materials, crosslinking agent concentration, adsorbent dosage, contact time, temperature, pH, and pollutant concentration systematically. The above studies indicated that the maximum adsorption capacity of 291.6 mg/g was obtained at pH = 5.1. The kinetic datas were well fitted to the pseudo-second-order model, indicating that chemical sorption was the rate-limiting step. The isotherm of adsorption could be described by the Langmuir-Freundlich model well, which showed that SK gel had heterogeneous surface and different binding sites. By analyzing FT-IR spectroscopy and the adsorption changes under different pH, the adsorption mechanism may be explained by hydrogen bonding and the electrostatic interactions between CIP and the adsorbent. This study highlighted that SK gel beads could be used as a promising adsorbent for the large-scale removal of CIP in aqueous solutions, and the research will be conducive to address CIP pollution efficiently. [ABSTRACT FROM AUTHOR]