Hexavalent chromium [Cr(VI)], one of the most toxic contaminants, is released in the environment due to various anthropogenic activities. Exposure of Cr(VI) can pose a serious threat to the public health as well as flora and fauna. Effective treatment of Cr(VI) is, therefore, very essential from safety, health, and environment points of view. The present review focuses on the development of silica-based materials for the adsorption of Cr(VI) from wastewater. After discussing toxicity issues and general removal methods of Cr(VI), the importance of silica materials are highlighted. The silica has different shapes, sizes, surface areas, and pore diameters and, hence, can play a vital role in designing the adsorbent. They can be modified into organic, inorganic, polymeric, biological, and ionic liquid based materials. Therefore, they are broadly classified into these five categories. The adsorption isotherms and kinetics of these materials for Cr(VI) are discussed and compared with each other. Future prospects based on the findings of the review article are summarized in the end which mainly emphasizes the importance of biosorbents and ionic liquid immobilized silica materials for the treatment of Cr(VI).

A novel bifunctional mesoporous organosilica, PEG-functionalized bis-prolinium chloride bridged mesoporous organosilica (BPBMO) was synthesized by reacting the precursor, PEG-functionalized bis-prolinium chloride bridged organosilane (BPRIL) with tetraethyl orthosilicate (TEOS) in the presence of surfactant. The chemical conformation of BPBMO was investigated by using Fourier transform infrared (FTIR), thermogravimentric analysis (TGA), 13C, and 29Si cross-polarization/magic angle spinning (CP/MAS) NMR techniques. The characterization represents PEG-linked-prolinium (−N+Cl–) and carboxyl (−COOH) entities, constructing the dicationic framework through siloxane (Si–O–Si) linkages. The pore-wall distribution and the periodicity of BPBMO retained during the synthesis were examined by small-angle X-ray scattering (SAXS), Brunauer-Emmett-Teller-Barrett-Joyner-Halenda (BET-BJH), and transmission electron microscopy (TEM) techniques. The results revealed BPBMO as a spherical shaped solid (50–100 nm) having mesopore channels hexagonally arranged with interparticle porosity (S BET = 487 m2/g and D BJH = 5.1 nm). The material has provided active binding sites for the simultaneous removal of NO3 – and Pb2+ ions when introduced in the aqueous solutions of Pb­(NO3)2 (50 mg/L, pH 6). The removal of NO3 – by ion-exchange with prolinium (−N+Cl–) entities and the electrostatic interaction of Pb2+ with carboxylate (−COO–) group were characterized by using Raman spectroscopy, ion chromatography, and X-ray photoelectron spectroscopy (XPS) technique. The maximum removal of NO3 – and Pb2+ ions were achieved within 1 h of the adsorption reaction. The adsorption has followed the Langmuir isotherm model with the adsorption capacities (q m) of 23.04 and 21.92 mg/g for NO3 – and Pb2+ ions, respectively. The efficiency of the adsorbent was also compared with other adsorbents. Further, the BPBMO material has depicted three consecutive adsorption/desorption cycles with negligible loss in the structural conformation.

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Porous liquid is a unique liquid medium that combines permanent porosity of porous solid with the uidity of liquid, and this special characteristic makes it potential in various applications. Here we report the rst photoresponsive porous ionic liquid (PPIL) by solubilizing photoresponsive metal-organic polyhedron (PMOP, constructed from dicopper and azobenzene-containing carboxylate) in polyethyleneglycol-functionalized bulky ionic liquid (IL). Owing to favorable ion interactions, bulky IL molecules encircle outside PMOP cages, and the inter cavities are maintained. The azobenzene moieties can be isomerized freely in the obtained PPILs to expose and shelter active sites upon visible and UV light irradiations. Hence, the adsorption capacity of PPILs is controllable by light irradiation, and the change in CO 2 uptake is up to 30% which is different from neat IL with negligible change. This study might inspire the development of new adsorption process regulated by light instead of conventional pressure and temperature swing adsorption technologies. Full TextPorous liquids have drawn increasing attention owing to the combination of porous solid and uid which furnishes resulting owing system eternal porosity. [1][2][3][4] The permanent pores endow uids with subsidiary physicochemical properties, rendering as suitable solitary media for a variety of applications like adsorption and catalysis. [5][6][7] Intrinsic cavities in uidic systems can be generated by three methods, that is, porous hosts' functionalization (type I) as well as their solubilization (type II) or dispersion (type III) in relatively size-excluded solvents. [8][9][10] In present, basic entities for rigid host structures are mostly from metal-organic frameworks, porous organic cages and zeolites, while chlorinated solvents and ionic liquids (ILs) are chosen as sterically hindered solvents. [11][12][13][14][15] Such combinations lead to the formation of a series of interesting porous liquids.Life systems are capable of modulating themselves to variable environments for survival. Inspiring by this, smart materials that can respond to external stimuli (e.g. temperature, light, and pH) with tunable features have been developed. [16][17][18][19][20] Among various external stimuli, light attracts great interest since it allows rapid and precise control with rare undesirable byproducts. [21][22][23][24] Azobenzene is a classic photoresponsive molecule, its con guration transformation between cis and trans isomer can be induced by ultraviolet (UV) and visible light irradiation. [25][26][27] On the basis of such con guration transformation, it is promising to construct azobenzene-based materials with tunable performance through sheltering and exposing active sites. [28][29][30][31][32] By introducing photoresponsive porous moieties to bulky liquids, it is expected to endow the uids with properties responsive to light. As a result, the adsorption process is possible to run by light irradiation, which is remotely controllable and much more energy-e cient in compar...

Ionic liquids (ILs) are playing increasingly important roles in the membrane separation processes. The present manuscript discusses the removal of Pb(II) ions from aqueous solution using an emulsion ionic liquid membrane (EILM) process. Initially, the emulsion liquid membrane (ELM) was prepared by stirring strip phase (sulphuric acid) and organic phase (surfactant: span 80, extractant: D2EHPA, diluent: hexane) together under high speed agitation. Note that, the parameters of the ELM process such as emulsification speed, pH of the feed phase, treat ratio, extractant and surfactant concentrations were studied for the maximum removal of Pb(II) ions. The role of IL was explored by adding hydrophobic IL, octylmethylimidazole hexafluorophosphine ([OMIM][PF 6 ]), in the organic phase. The performance of ELM with and without IL was compared on the basis of stability, enrichment factor and the removal efficiency for Pb(II). The results showed that the percentage of Pb(II) extraction was complete by the emulsion membrane with IL (EILM) in comparison to the 97% achieved by neat ELM. Further, the stability and the enrichment factor of the EILM were found to be 2-3 times greater than that of the ELM. The FT-IR spectroscopic analysis revealed that bond interactions between IL and membrane phase components avoided the coalescence of internal phase droplets and enhanced the emulsion stability. The results obtained in this work support the use of the IL [OMIM][PF 6 ] as both a stabilizer and carrier for the overall improvement of the ELM process.