Effective removal of Cr (VI) from aqueous solution by reinforced sodium alginate/polyethyleneimine/graphene oxide composite aerogels

A reinforced composite aerogel absorbent was synthesized using a green chemistry method and an environmentally friendly freeze-drying technique. The absorbent consisted of sodium alginate, polyethyleneimine (PEI), and graphene oxide (GO). The ability of the absorbent to remove Cr (VI) ions from aqueous solutions was studied. PEI was a nitrogen source for Cr (VI) removal and a cross-linking agent for GO sheets, while SA was a reinforcing material. The aerogel was investigated using X-ray diffraction, scanning electron microscopy, Fourier transform infrared (FTIR) spectroscopy, texture analysis, Raman spectroscopy, and thermogravimetric analysis (TGA). Batch studies were conducted to investigate the effect of pH and contact time on adsorption. The results indicated that the SA/PEI/GO aerogel had a maximum adsorption capacity of 174.05 mg·g-1 for Cr (VI) at pH 2. The adsorption mechanism was described using the Langmuir isotherm and pseudo-second-order kinetic models. Thermodynamic studies revealed that the adsorption process was spontaneous and endothermic. The aerogel demonstrated good regeneration ability and satisfactory recovery for Cr (VI) even after five cycles. These findings suggest that the composite aerogel could be a promising adsorbent for efficiently removing Cr (VI) from wastewater.

Progress in surface-modified silicas for Cr(VI) adsorption: A review

Various toxic chemicals are discharging to the environment due to rapid industrialization and polluting soil, water, and air causing numerous diseases including life-threatening cancer. Among these pollutants, Cr(VI) or hexavalent chromium is one of the most carcinogenic and toxic contaminants hostile to human health and other living things. Therefore, along with other contaminants, the removal of Cr(VI) efficiently is very crucial to keep our environment neat and clean. On the other hand, silica has a lot of room to modify its surfaces as it is available with various sizes, shapes, pore sizes, surface areas etc. and the surface silanol groups are susceptible to design and prepare adsorbents for Cr(VI). This review emphases on the progress in the development of different types of silica-based adsorbents by modifying the surfaces of silica and their application for the removal of Cr(VI) from wastewater. Toxicity of Cr(VI), different silica surface modification processes, and removal techniques are also highlighted. The adsorption capacities of the surface-modified silica materials with other parameters are discussed extensively to understand how to select the best condition, silica and modifiers to achieve optimum removal performance. The adsorption mechanisms of various adsorbents are also discussed. Finally, future prospects are summarized and some suggestions are given to enhance the adsorption capacities of the surface-modified silica materials.

Enhanced adsorption of hexavalent chromium and the microbial effect on quartz sand modified with Al-layered double hydroxides

To enhance the hexavalent chromium (Cr(VI)) removal performance of simulated constructed rapid infiltration systems (CRIS) with quartz sand (QS) substrate, QS coated with Al-layered double hydroxides (Al-LDHs@QS) was prepared by the co-precipitation method under alkaline conditions. A scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD) were used to characterize QS before and after modification. The result showed that the Al-LDHs were successfully coated on the surface of the QS. The isotherm adsorption experiment indicated that compared with the original QS, the adsorption property of the modified QS changed from monolayered chemical adsorption to multilayered physical adsorption, perhaps because of different types of adsorption forces. Moreover, the adsorption capacity of modified QS was significantly enhanced and ZnAl-LDHs@QS had a maximum adsorption capacity (1428.57 mg·kg^-1) nearly 6 times greater than that of the original QS (232.56 mg·kg^-1). Adsorption experiments at different pH showed that the adsorption capacity of ZnAl-LDHs@QS gradually increased as acidity decreased. High-throughput sequencing revealed that the relative abundance of chrome-tolerant microorganisms at the phylum and family levels were increased in modified QS compared with original QS. Hemocytometer counting revealed enhanced microbial quantity on the surface of QS after modification. The content of extracellular polymeric substances (EPS) and the enzymatic activity of the microorganisms adhered to the surface of modified and original QS were detected, results showed that Al-LDHs had an obvious influence on the promotion of EPS secretion and enhanced the enzymatic activity of microorganisms. These changes indicated that the modified QS created better conditions for microorganism growth, and the improved microbial effect caused strong biosorption, resulting in greatly enhanced Cr(VI) removal. Thus, ZnAl-LDHs@QS is a better choice for CRIS to remove Cr(VI).

Removal of Arsenic, Chromium and Uranium from Water Sources by Novel Nanostructured Materials Including Graphene-Based Modified Adsorbents: A Mini Review of Recent Developments

Groundwater is commonly used as a drinking water resource all over the world. Therefore, groundwater contamination by toxic metals is an important issue of utmost concern for public health, and several technologies are applied for their effective removal, such as coagulation, ion exchange, adsorption, and membrane applications like reverse osmosis. Adsorption is acknowledged as a simple, effective and economic technology, which has received increased interest recently, despite certain limitations regarding operational applications. The respective scientific efforts have been specifically focused on the development and implementation of novel nano-structured adsorbent materials, which may offer extensive specific surface areas, much higher than the conventional adsorbents, and hence, are expected to present higher removal efficiencies of pollutants. In this paper, the recent developments of nanomaterial applications for arsenic, chromium and uranium removal from groundwaters are critically reviewed. Particularly, the use of novel composite materials, based mainly on hybrid metallic oxide nanoparticles and on composites based on graphene oxide (GO) (i.e., graphene-based hybrids), showed promising evidences to achieve efficient removal of toxic metals from water sources, even in full scale applications.

Graphene oxide-based materials for efficient removal of heavy metal ions from aqueous solution: A review

Graphene with atomic layer of sp²-hybridized carbon atoms in a hexagonal structure has attracted multidisciplinary attention since its discovery. Due to the inherent advantages of large specific surface area and abundant functional groups, its derivative graphene oxide (GO) nanomaterials have achieved large-scale development in effective pollution treatment. In the past few years, novel GO-based nanomaterials through coupling with other nanomaterials have been synthesized with significant process and applied for efficient elimination of different kinds of pollutants. This paper aims to summarize recent research results on the excellent removal ability of GO-based nanomaterials for various heavy metal ions in aqueous solutions. The synthesis, adsorption process characteristics and interaction mechanism of the adsorbent are emphasized and discussed. The effects of various environmental conditions are outlined. At last, a brief summary, perspective and outlook are presented. This review is intended to provide some thrilling information for the design and manufacture of GO-based nanomaterials for the elimination of heavy metal ions from wastewater in environmental pollution management.

Artificial inorganic biohybrids: The functional combination of microorganisms and cells with inorganic materials

Biohybrids can be defined as the functional combination of proteins, viable cells or microorganisms with non-biological materials. This article reviews recent findings on the encapsulation of microorganisms and eukaryotic cells in inorganic matrices such as silica gels or cements. The entrapment of biological entities into a support material is of great benefit for processing since the encapsulation matrix protects sensitive cells from shear forces, unfavourable pH changes, or cytotoxic solvents, avoids culture-washout, and simplifies the separation of formed products. After reflecting general aspects of such an immobilization as well as the chemistry of the inorganic matrices, we focused on manufacturing aspects and the application of such biohybrids in biotechnology, medicine as well as in environmental science and for civil engineering purpose.

STATEMENT OF SIGNIFICANCE

The encapsulation of living cells and microorganisms became an intensively studied and rapidly expanding research field with manifold applications in medicine, bio- and environmental technology, or civil engineering. Here, the use of silica or cements as encapsulation matrices have the advantage of a higher chemical and mechanical resistance towards harsh environmental conditions during processing compared to their polymeric counterparts. In this perspective, the article gives an overview about the inorganic material systems used for cell encapsulation, followed by reviewing the most important applications. The future may lay in a combination of the currently achieved biohybrid systems with additive manufacturing techniques. In a longer perspective, this would enable the direct printing of cell loaded bioreactor components.

Nitrogen-containing amino compounds functionalized graphene oxide: Synthesis, characterization and application for the removal of pollutants from wastewater: A review

Nowadays, using graphene oxide (GO) as an adsorbent for removing pollutants from wastewater has attracted increasing attention due to its unique physic-chemical properties. Nitrogen-containing amino (NA) compounds have excellently complexing properties due to their abundant amino functional groups. In order to obtain an innovative adsorbent, functionalized GO (NAGO) has been developed by combining the properties of GO with the advantages of NA compounds. The obtained NAGO composites usually exhibit great improvement in adsorption properties and can be used as a promising adsorbent for decontamination of wastewater. This paper reviewed recent progress of synthetic technologies about fabricating various NAGOs, and their morphologies, structures and functional characteristics. Meanwhile, important applications of NAGOs for different kind of pollutants and theory of the adsorption phenomena are discussed based on the isothermal and kinetic adsorption models. Furthermore, the affecting factors, underlying mechanisms and comparison with other adsorbents for the removal of pollutants are reviewed. Conclusively, the perspectives and challenges involved in the application of NAGOs for decontamination of wastewater have also been proposed to promote sustainable development of this new exciting field.

A bio-hybrid material for adsorption and degradation of phenanthrene: bacteria immobilized on sawdust coated with a silica layer

Membrane permeability of bacteria immobilized in silica-coated sawdust was increased, and its metabolic activity toward Phe was enhanced.

Alginate/porous silica matrices for the encapsulation of living organisms: tunable properties for biosensors, modular bioreactors, and bioremediation devices

The encapsulation of living cells within inorganic silica hydrogels is a promising strategy for the design of biosensors, modular bioreactors, and bioremediation devices, among other interesting applications, attracting scientific and technological interest. These hostguest multifunctional materials (HGFM) combine synergistically specific biologic functions of their guest with those of the host matrix enhancing their performance. Although inorganic immobilization hosts present several advantages over their (bio)polymer-based counterparts in terms of chemical and physical stability, the direct contact of cells with silica precursors during synthesis and the constraints imposed by the inorganic host during operating conditions have proved to influence their biological response. Recently, we proposed an alternative two-step procedure including a pre-encapsulation in biocompatible polymers such as alginates in order to confer protection to the biological guest during the inorganic and more cytotoxic synthesis. By means of this procedure, whole cultures of microorganisms remain confined in small liquid volumes generated inside the inorganic host, providing near conventional liquid culture conditions.Moreover, the fact of protecting the biological guest during the synthesis of the host, allows extending the synthesis parameters beyond biocompatible conditions, tuning the microstructure of the matrix. In turn, the microstructure (porosity at the nanoscale, radius of gyration of particles composing the structure, and fractal dimension of particle clusters) is determinant of macroscopic parameters, such as optical quality and transport properties that govern the encapsulation material’s performance. Here, we review the most interesting applications of the two-step procedure, making special emphasis on the optimization of optical, transport and mechanical properties of the host as well as in the interaction with the guest during operation conditions.

Prospective application of Aspergillus species immobilized in sodium montmorillonite to remove toxic hexavalent chromium from wastewater

Aspergillus BRVR immobilized in sodium montmorillonite for the effective removal of Cr(vi) from waste water.

A novel template free synthetic strategy to graphene–iron oxide nanotube hybrid

A magnetically separable graphene–iron oxide nanotube composite was synthesised for the first time via an adept template free hydrothermal route.

Preparation of magnetic ionic liquid/chitosan/graphene oxide composite and application for water treatment

Magnetic chitosan and graphene oxide-ionic liquid (MCGO-IL) composites as biodegradable biosorbents were synthesized by impregnating MCGO with ionic liquid. The characteristic results of FTIR, SEM, and XRD showed that MCGO-IL were successfully prepared with large surface area and good magnetic responsiveness. They were used for the removal of Cr(VI) from simulated wastewater with a fast solid-liquid separation in the presence of external magnetic field. The influence of various analytical parameters on the adsorption of Cr(VI) such as pH, contact time, and initial ion concentration were studied in detail. The adsorption followed a pseudo-second-order kinetics. The equilibrium adsorption was well-described by the Langmuir isotherm mode and the maximum adsorption capacity was 145.35 mg/g. The stronger intermolecular hydrogen bond between MCGO-IL and Cr(VI) and the hydroxyl and amine groups were believed to be the metal ion binding sites. Moreover, the MCGO-IL could be repeatedly used by simple treatment without obvious structure and performance degradation. The obtained results indicated that the impregnation of the room temperature IL significantly enhances the removal efficiency of Cr(VI). The MCGO-IL may be suitable materials in heavy metal ion pollution cleanup if they are synthesized in large scale and at low price in near future.

Chromium(VI) removal via reduction-sorption on bi-functional silica adsorbents

Organically-modified silica gels bearing mercaptopropyl and ethylenediaminetriacetate groups (SiO2-SH/ED3A) have been used for reduction and subsequent sequestration of Cr(VI) species. The uptake mechanism involves Cr(VI) reduction by thiol groups (SH) and further immobilization of the so-generated Cr(III) species via complexation to the ethylenediaminetriacetate moieties (ED3A). The most appropriate pH range (1-3) for complete Cr(VI) reduction-sorption by SiO2-SH/ED3A originates from the balance between full reduction of Cr(VI) by SH, requiring low pH values, and quantitative complexation of Cr(III) by ED3A, which is favored in less acidic media. Such bi-functional adsorbents are considerably more effective at removal of Cr(VI) than those simply modified with thiol groups alone. The whole reduction-sorption process was characterized by fast kinetics, thus permitting efficient use of the SiO2-SH/ED3A adsorbent in dynamic conditions (column experiments). Monitoring the amount of immobilized chromium species on the solid was achieved using X-ray fluorescence spectroscopy and UV-vis spectroscopy. Studying the influence of ionic strength and presence of heavy metals revealed few interference on Cr(VI) removal.

Batch and continuous flow studies of adsorptive removal of Cr(VI) by adapted bacterial consortia immobilized in alginate beads

The adsorptive removal of Cr(VI) by alginate beads containing Cr(VI)-adapted Acinetobacter junii, Escherichia coli and Bacillus subtilis in batch and continuous packed bed column reactors was investigated. Under optimized conditions (pH 3.0; contact time, 180 min; 30 °C; initial Cr(VI) concentration of 100 mg/L), 65.86 mg/g adsorption capacity was recorded in the batch study. When an adsorbent dosage of 1g/L, a flow rate of 5 mL/min, a bed height of 20 cm, an initial Cr(VI) concentration of 300 mg/L was employed, a capacity of 657 mg/g was noted for the continuous column assay. The batch sorption data followed the Langmuir isotherm and pseudo second order kinetics. Five sorption/desorption cycles yielded 100%, 99.63%, 95.31%, 80.7% and 74.22% regeneration, respectively. Cr(VI) adsorption studies using spiked ground water, freshwater and domestic wastewater in a packed bed reactor demonstrated Cr(VI) removals of 64.8%, 55.08%, 56.86% respectively. Cr(VI) sorption on immobilized bacteria was confirmed with Fourier-transform infrared and Energy dispersive X-ray spectroscopy.