Chemical modification of silica surface by immobilization of functional groups for extractive concentration of metal ions

Two Birds with One Stone Strategy: Simultaneous Removal of Cr(VI) and Cr(III) Efficiently by Porous ZnIn2S4/SBA-15 Nanorods

Carcinogen Cr(VI) is reduced efficiently into Cr(III) by a photocatalyst, but the produced Cr(III) is difficult to transfer from the photocatalytic active site. The "two birds with one stone" strategy is proposed to realize the in situ growth of ZnIn2S4 nanoplates on SBA-15 and the creation of separated active sites, in which ZnO loading on the porous SBA-15 nanorod was used as a zinc source. Obtained samples ZnIn2S4/SBA-15 (ZIS/SBA) showed the redshift of the absorption band and better separation of photoinduced carriers than pristine ZnIn2S4, due to its smaller size and S defect. All of the Cr(VI) was reduced to Cr(III) by the ZIS/SBA sample during the photocatalytic process, which was 2 times higher than pristine ZnIn2S4. Moreover, 92.8% of Cr(III) was adsorbed simultaneously during photocatalysis due to the electrostatic interaction from SBA-15. In addition, the ZIS/SBA sample showed good recycling stability after 5 times cycles, providing a new strategy for the in situ growth of ZnIn2S4 on the surface of porous materials and a novel way for the simultaneous removal of Cr(VI) and Cr(III) during photocatalysis.

Enhanced platinum and palladium recovery from aqueous solutions: a comparative study of acylthiourea and amine-modified silica gel adsorbents

The recovery of precious metals from secondary sources is becoming increasingly important due to their natural scarcity and rising industrial demand. This study introduces a novel adsorbent, N-triethoxysilylpropyl-N'-benzoylthiourea-modified silica gel (TESP-BT-SG), developed for the selective recovery of platinum (Pt) and palladium (Pd) from aqueous solutions that simulate refinery wastewater. The extraction capabilities of TESP-BT-SG were compared with those of an amine-bearing adsorbent, (3-aminopropyl)triethoxy-silane-modified silica gel (APTES-SG), previously recognized for Pt and Pd recovery. Under optimal conditions, TESP-BT-SG achieved extraction efficiencies of 97% for Pt and 99% for Pd. Both adsorbents demonstrated rapid adsorption kinetics for Pd relative to Pt, reaching equilibrium within 3 hours for Pd and within 6 hours (TESP-BT-SG) and 24 hours (APTES-SG) for Pt. In solutions with elevated competing ion concentrations (5-100 mg L-1), both adsorbents retained high selectivity (>97%) for Pt and Pd. Adsorption isotherms and kinetic models were applied to elucidate the adsorption mechanisms, with the Langmuir isotherm and pseudo-second-order models providing the best fits, indicating monolayer coverage and chemisorption, respectively. Notably, the APTES-SG sorbent demonstrated enhanced performance with an increased loading capacity of 2.45 mmol g-1 compared to the previously reported 1.15 mmol g-1, achieved through our improved synthesis method. This modified APTES-SG showed significantly higher affinity for Pd (98%), Pt (97%), and iridium (Ir) (89%) compared to previous values of 8%, 33%, and 42%, respectively. The exceptional efficiency and selectivity of these silica-anchored adsorbents underscore their potential as cost-effective solutions for industries seeking to recover precious metals.

Recent advances in heavy metals uptake by tailored silica-based adsorbents

In the last decade, numerous designed adsorbent materials like metal-organic frameworks (MOFs), covalent organic frameworks (COF), carbon nanotubes (CNTs), etc. have been developed and investigated for metal ions extraction applications in the contaminated aquatic environment. These materials are facing the problems associated with large-scale production, cost, stability, and reusable. Conventional adsorption like carbon and silica is still valuable and is in use for industrial applications. In the last decade, silica has gone through a lot of alteration and modification to enhance its efficiency for heavy metal adsorption. In this review, the tailoring of the silica properties by surface functionalization or developing new hybrid composites for the scavenging of the heavy have been summarized. Silica functionalization with various organic functional groups, composites like silica/polymers, silica/metal oxide, silica aerogels, etc., has been explored. Moreover, interpretations of the effective metal uptake mechanisms associated with metal ions adsorption onto silica adsorbents are also investigated. Overall, the review offers comprehensive insights into the interface between metal ions and silica-based materials.

Efficient Removal of Mercury from Wastewater Solutions by a Nitrogen-Doped Hyper-Crosslinked Polyamine

Mercury, a highly toxic metal and pollutant, poses a significant risk to human health and the environment. This study describes the synthesis of a new nitrogen-doped heteroaromatic hyper-crosslinked polyamine (HCPA) via the polycondensation of 2,6-diaminopyrazine and tris(4-formylphenyl)amine for the efficient removal of mercury ions from aqueous solutions. The HCPA polymer was characterized by solid-state 13C-NMR and FT-IR spectroscopy. A powder X-ray diffraction and thermogravimetric analysis showed that the polymer was semicrystalline in nature and stable up to 500 °C. Adsorption isotherms indicated that mercury adsorption occurred via mono- and multilayer adsorption by HCPA, as depicted by the Langmuir, Freundlich, and Redlich-Peterson isotherm models, with a maximum adsorption capacity of qm = 333.3 mg/g. Adsorption kinetic models suggested that the adsorption process was fast and effective, reaching equilibrium within 20 min. Thermodynamics of the adsorption process revealed that it was endothermic and spontaneous in nature due to the positive ΔH0 of 48 kJ/mol and negative ΔG0 values of -4.5 kJ/mol at 293 K. Wastewater treatment revealed 98% removal of mercury indicating the selective nature of HCPA. Finally, HCPA exhibited excellent performance and regeneration up to three cycles, demonstrating its great potential as an adsorbent for environmental remediation applications.

Nano silica's role in regulating heavy metal uptake in Calendula officinalis

BACKGROUND

Soil contamination with heavy metals poses a significant threat to plant health and human well-being. This study explores the potential of nano silica as a solution for mitigating heavy metal uptake in Calendula officinalis.

RESULTS

Greenhouse experiments demonstrated, 1000 mg•kg- 1 nano silica caused a 6% increase in soil pH compared to the control treatment. Also in 1000 mg. kg- 1 nano silica, the concentrations of available Pb (lead), Zn (zinc), Cu (copper), Ni (nickel), and Cr (chromium) in soil decreased by 12%, 11%, 11.6%, 10%, and 9.5%, respectively, compared to the control. Nano silica application significantly reduces heavy metal accumulation in C. officinalis exposed to contaminated soil except Zn. In 1000 mg.kg- 1 nano silica shoots Zn 13.28% increased and roots Zn increased 13% compared to the control treatment. Applying nano silica leads to increase the amount of phosphorus (P) 25%, potassium (K) 26% uptake by plant, In 1000 mg.kg - 1 treatment the highest amount of urease enzyme activity was 2.5%, dehydrogenase enzyme activity, 23.6% and the highest level of alkaline phosphatase enzyme activity was 13.5% higher than the control treatment.

CONCLUSION

Nano silica, particularly at a concentration of 1000 mg.kg - 1, enhanced roots and shoots length, dry weight, and soil enzyme activity Moreover, it increased P and K concentrations in plant tissues while decreasing heavy metals uptake by plant.

Postharvest handling of ethylene with oxidative and absorptive means

Fruit ripening is an unfolding of a series of genetically-programmed modifications and tend to be highly orchestrated irrevocable phenomenon mediated by ethylene. Phytohormone ethylene also leads to over-ripening, senescence, loss of texture, microbial attack, reduced post-harvest life and other associated problems during storage and transportation of fruits. Its harmful impacts on fresh fruits, vegetables, and ornamentals result in substantial product losses even up to 80%. Curbing of this inevitable menace is therefore need of the hour. Accrual of ethylene in packaging system should fundamentally be ducked to extend the shelf-life and uphold an adequate superiority of perishables in visual and organoleptic terms. The current review discusses about properties, factors affecting and impact of ethylene, intimidation of its impact at gene vis-à-vis activity level using gene-modification/inhibition techniques, chemical/physical in conjunction with other suitable approaches. It also entails the most commercially cultivated approaches worldwide viz. KMnO4-based oxidation together with adsorption-based scrubbing of ethylene in thorough details. Future ethylene removal strategies should focus on systematic evaluation of KMnO4-based scavenging, exploring the mechanism of adsorption, adsorbent(s) behavior in the presence of other gases and their partial pressures, volatiles, temperature, relative humidity, development of hydrophobic adsorbents to turn-up under high RH, regeneration of adsorbent by desorption, improvement in photocatalytic oxidation etc. and further improvements thereof.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05777-1.

Advancements in sustainable platinum and palladium recovery: unveiling superior adsorption efficiency and selectivity with a novel silica-anchored acylthiourea adsorbent

This study addresses the pressing issue of depleting natural resources of platinum group metals (PGMs), driven by their widespread use in modern applications and increasing demand for renewable energy technologies. With conventional sources dwindling, the search for economically viable recovery methods from alternative sources has become crucial. Our focus was on innovating efficient recovery strategies, leading to the development of two novel silica-anchored adsorbents: DTMSP-BT-SG, a highly efficient acylthiourea adsorbent, and BTMSPA-SG, a silica-anchored amine adsorbent. We conducted comprehensive experiments under PGM mining wastewater conditions, varying parameters such as adsorbent mass, pH, concentration, contact time, competing ions, and volume. DTMSP-BT-SG demonstrated exceptional performance, achieving maximum adsorption efficiencies of >98% for Pt and >99% for Pd at pH 2, 0.5 g L-1 dosage, and 5 mg L-1 concentration. In contrast, under the same conditions, BTMSPA-SG recovered <56% and <89% of Pt and Pd, respectively. The experimental data for both adsorbents were analysed using Langmuir and Freundlich isotherm models for concentration and pseudo-first and second-order models for contact time. The Langmuir model best described the adsorption data, indicating homogenous monolayer adsorption of Pt and Pd. The kinetic models suggested a pseudo-second-order process, implying chemisorption. Furthermore, in the presence of competing ions and other PGMs, DTMSP-BT-SG exhibited significantly higher recovery rates for Pt and Pd compared to BTMSPA-SG. Overall, DTMSP-BT-SG emerged as a more selective and efficient adsorbent across varied parameters. Its exceptional adsorption efficiency, coupled with cost-effectiveness, positions it as a promising and competitive recovery agent for extracting PGMs from mining wastewaters.

Ions Adsorbed at Amorphous Solid/Solution Interfaces Form Wigner Crystal-like Structures

When a surface is immersed in a solution, it usually acquires a charge, which attracts counterions and repels co-ions to form an electrical double layer. The ions directly adsorbed to the surface are referred to as the Stern layer. The structure of the Stern layer normal to the interface was described decades ago, but the lateral organization within the Stern layer has received scant attention. This is because instrumental limitations have prevented visualization of the ion arrangements except for atypical, model, crystalline surfaces. Here, we use high-resolution amplitude modulated atomic force microscopy (AFM) to visualize in situ the lateral structure of Stern layer ions adsorbed to polycrystalline gold, and amorphous silica and gallium nitride (GaN). For all three substrates, when the density of ions in the layer exceeds a system-dependent threshold, correlation effects induce the formation of close packed structures akin to Wigner crystals. Depending on the surface and the ions, the Wigner crystal-like structure can be hexagonally close packed, cubic, or worm-like. The influence of the electrolyte concentration, species, and valence, as well as the surface type and charge, on the Stern layer structures is described. When the system parameters are changed to reduce the Stern layer ion surface excess below the threshold value, Wigner crystal-like structures do not form and the Stern layer is unstructured. For gold surfaces, molecular dynamics (MD) simulations reveal that when sufficient potential is applied to the surface, ion clusters form with dimensions similar to the Wigner crystal-like structures in the AFM images. The lateral Stern layer structures presented, and in particular the Wigner crystal-like structures, will influence diverse applications in chemistry, energy storage, environmental science, nanotechnology, biology, and medicine.

Advances of polymer microspheres and its applications for enhanced oil recovery

After long-term water injection, mature reservoirs are encountered with the adverse consequences of the treatment, including erosion, rock formation destruction and drastic decline in oil recovery rate for the past years. Today, the inexpensive and highly efficient polymer microspheres can be considered as a solution to the current issue with excess water production. Studies on practical utilization of polymer microspheres to plug high-permeability zones in heterogeneous reservoirs gained immense popularity in oil production lately. This review aims to give classification to polymer microspheres, including fluorescent polymer microspheres, low elastic polymer microspheres, viscoelastic polymer microspheres and nano-composite polymer microspheres and discuss the specific structural and behavioral traits of each polymer microsphere. Differences in preparation methods, comparisons of performance evaluation and oil recovery rate assessment were also studied. The current complications with functional application of polymer microspheres and its further improvements were considered. This review will provide assistance to the researchers with further advancements of the polymer microspheres, by effectively increasing the oil recovery levels in heterogeneous reservoirs, which will also meet the economical and ecological requirements of the oilfields.

Poly(2-vinylpyridine)/MCM-41 Composites with Micropores and Switchable Mesopores for the Removal of Cr(VI)

Porous structure design and reversible regulation of pore size during adsorption-desorption are crucial to the removal of pollutants in water such as Cr(VI). In this paper, micropores and switchable mesopores were constructed on MCM-41 to further improve adsorption-desorption performance of Cr(VI) via the confinement effect of micropores and opening and closing of mesopores. 2-Vinylpyridine was introduced and polymerized into the pores and on the pore mouth of MCM41 modified by C═C group (AM41) under the irradiation of ultraviolet light. The obtained samples (PM41) possessed mesopores (2.73 nm) and micropores (1.36 nm), where mesopores could open or close under different pH and micropores showed the confinement effect because their pore size is close to Cr(VI) diameter (0.87 nm). Compared with MCM-41, the introduction of poly(2-vinylpyridine) enhanced obviously its adsorptive ability and it trapped most of the Cr(VI) (99%) in solution, 12 times higher than that of the parent sample. The change of pore size is favorable to the cycle performance, and after 3 times recycling, the removal rate of Cr(VI) by PM41-20 remained above 88%. Langmuir isotherm showed a better data correlation than the Freundlich model. Cr(VI) in solution was removed by electrostatic interaction between the pyridine group and Cr(VI) and the confinement effect from micropores.

Loading of Silver (I) Ion in L-Cysteine-Functionalized Silica Gel Material for Aquatic Purification

The L-cysteine-functionalized silica (SG-Cys-Na+) matrix was effectively loaded with silver (I) ions using the batch sorption technique. Optimal Ag(I) loading into SG-Cys-Na+ reached 98% at pHi = 6, 80 rpm, 1 mg L-1, and a temperature of 55 °C. The Langmuir isotherm was found to be suitable for Ag(I) binding onto SG-Cys-Na+ active sites, forming a homogeneous monolayer (R2 = 0.999), as confirmed by FTIR spectroscopy. XRD analysis indicated matrix stability and the absence of Ag2O and Ag(0) phases, observed from diffraction peaks. The pseudo-second-order model (R2 > 0.999) suggested chemisorption-controlled adsorption, involving chemical bonding between silver ions and SG-Cys-Na+ surface. Thermodynamic parameters were calculated, indicating higher initial concentrations leading to increased equilibrium constants, negative ΔG values, positive ΔS values, and negative ΔH. This study aimed to explore silver ion saturation on silica surfaces and the underlying association mechanisms. The capability to capture and load silver (I) ions onto functionalized silica gel materials holds promise for environmental and water purification applications.

Rational design of selective functionalized silica adsorbents for Hg(II) removal from FGD wastewater. A combined experimental and theoretical study

The binding of Hg2+ by mercaptan-functionalized silica possessing different physical characteristics was explored through experimental investigations and theoretical calculations. The impacts of the pore structure of silica adsorbents on functionalization and the kinetics of Hg2+ adsorption were also studied. The mechanism of Hg2+ adsorption was proposed based on the results of experimental and theoretical studies. The DFT calculations suggested a simultaneous monodentate and bidentate Hg2+ complex formation on sulfur-containing surface functional groups that strongly depends on the Hg2+ concentration. Theoretical Hg2+ adsorption isotherms predicted by DFT calculations have shown that even when the adsorbent surface had heterogeneous adsorption sites capable of simultaneous monodentate and bidentate complexation, the adsorption still followed the Langmuir model.

Slippery lubricant-infused silica nanoparticulate film processing for anti-biofouling applications

Microbial biofilm build-up in water distribution systems can pose a risk to human health and pipe material integrity. The impact is more devastating in space stations and to astronauts due to the isolation from necessary replacement parts and medical resources. As a result, there is a need for coatings to be implemented onto the inner region of the pipe to minimize the adherence and growth of biofilms. Lubricant-infused surfaces has been one such interesting material for anti-biofouling applications in which their slippery property promotes repellence to many liquids and thus prevents bacterial adherence. Textured and porous films are suitable substrate candidates to infuse and contain the lubricant. However, there is little investigation in utilizing a nanoparticulate thin film as the substrate material for lubricant infusion. A nanoparticulate film has high porosity within the structure which can promote greater lubricant infusion and retention. The implementation as a thin film structure aids to reduce material consumption and cost. In our study, we utilized a well-studied nanoporous thin film fabricated via layer-by-layer assembly of polycations and colloid silica and then calcination for greater stability. The film was further functionalized to promote fluorinated groups and improve affinity with a fluorinated lubricant. The pristine nanoporous film was characterized to determine its morphology, thickness, wettability, and porosity. The lubricant-infused film was then tested for its lubricant layer stability upon various washing conditions and its performance against bacterial biofilm adherence as a result of its slippery property. Overall, the modified silica nanoparticulate thin film demonstrated potential as a base substrate for lubricant-infused surface fabrication that repelled against ambient aqueous solvents and as an anti-biofouling coating that demonstrated low biofilm coverage and colony forming unit values. Further optimization to improve lubricant retention or incorporation of a secondary function can aid in developing better coatings for biofilm mitigation.

A comprehensive review of anionic azo dyes adsorption on surface-functionalised silicas

Surface -functionalised silica networks are advanced adsorbents. They have been given much attention for treating wastewater using the adsorption technique due to the silanol reactivity, resulting in strong binding affinities towards many pollutants. This review discusses the removal of anionic azo dyes utilising various functional groups such as amines, surfactants, polymers, macrocyclic, and other chelating groups functionalised on silica's surface. This review also reveals the steadily increasing interest in surface-functionalised silicas as adsorbents, emphasising the scholarly advancements in this field as a platform for future research. For that, adsorption capacities with different experimental conditions have been compared. The possible adsorption mechanisms, rate-limiting step, and factors affecting the anionic azo dye adsorption process have been comprehensively discussed. This review discloses that adsorbent characteristics such as porosity and functional groups, besides structural properties of an anionic azo dye, significantly affect adsorption. The adsorption process followed the Langmuir isotherm and pseudo-second-order models, with a predominantly spontaneous and endothermic nature. Multiple interactions, including electrostatic interaction, π-π interactions, and hydrogen bonding, are observed between dyes and functionalised silicas, indicating the adsorption process's complexity. Regeneration and cost-economic analysis are also presented to provide a roadmap for sustainable improvements. Chemical and biological regeneration techniques restore > 80% of the spent functionalised silicas. There is a significant opportunity to improve their efficiencies and regenerability, resulting in surface-functionalised silicas being used commercially instead of only in the laboratory. Finally, future research has been proposed by identifying current research gaps, particularly concerning the application of functionalised silicas in wastewater treatment.

Physicochemical, structural analysis of coal discards (and sewage sludge) (co)-HTC derived biochar for a sustainable carbon economy and evaluation of the liquid by-product

This study focused on the hydrothermal treatment (HTC) of coal tailings (CT) and coal slurry (CS) and the co-hydrothermal treatment (Co-HTC) of CT, CS and sewage sludge to assess the potential for increasing the carbon content of the hydrochar produced as an enabler for a sustainable carbon economy. The optimal combination methodology and response surface methodology were used to study the relationship between the important process parameters, namely temperature, pressure, residence time, the coal-to-sewage-sludge ratio, and the carbon yield of the produced hydrochar. The optimized conditions for hydrochar from coal tailing (HCT) and hydrochar from coal slurry (HCS) (150 °C, 27 bar, 95 min) increased fixed carbon from 37.31% and 53.02% to 40.31% and 57.69%, respectively, the total carbon content improved from 42.82 to 49.80% and from 61.85 to 66.90% respectively whereas the ash content of coal discards decreased from 40.32% and 24.17% to 38.3% and 20.0% when compared CT and CS respectively. Optimized Co-HTC conditions (208 °C, 22.5bars, and 360 min) for Hydrochar from the blend of coal discards and sewage sludge (HCB) increased the fixed carbon on a dry basis and the total carbon content from 38.67% and 45.64% to 58.82% and 67.0%, when compared CT and CS respectively. Carbonization yields for HCT, HCS, and HCB were, respectively, 113.58%, 102.42%, and 129.88%. HTC and Co-HTC increase the calorific value of CT and CS, to 19.33 MJ/kg, 25.79 MJ/kg, respectively. The results further show that under Co-HTC conditions, the raw biomass undergoes dehydration and decarboxylation, resulting in a decrease in hydrogen from 3.01%, 3.56%, and 3.05% to 2.87%, 2.98%, and 2.75%, and oxygen from 8.79%, 4.78, and 8.2% to 5.83%, 2.75%, and 6.00% in the resulting HCT, HCS, and HCB, respectively. HTC and Co-HTC optimal conditions increased the specific surface area of the feedstock from 6.066 m²/g and 6.37 m²/g to 11.88 m²/g and 14.35 m²/g, for CT and CS, respectively. Total pore volume rose to 0.071 cm³/g from 0.034 cm³/g, 0.048 cm³/g, and 0.09 cm³/g proving the ability of HTC to produce high-quality hydrochar from coal discards alone or in conjunction with sewage sludge as precursors for decontamination of polluted waters, soil decontamination applications, solid combustibles, energy storage, and environmental protection.

Characterization and Modification of Red Mud and Ferrosilicomanganese Fines and Their Application in the Synthesis of Hybrid Hydrogels

In this work, hybrid hydrogels were synthesized with the inclusion of two types of clay materials that are considered industrial waste: red mud (RM) and ferrosilicomanganese fines (FeSiMn). These solid waste materials were characterized by studying their particle size and chemical composition, which are two key variables for their application in the synthesis of hybrid hydrogels. The morphology imaged by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), showed, in the case of RM, heterogeneous size and shape particles, with 73% of the particles having lengths of less than 5 μm. On the other hand, FeSiMn had particles with a circular morphology of nanometric sizes. Regarding the synthesis of the hybrid hydrogels, it was determined that the incorporation of small percentages (0.1%) of the inorganic phases improved the capacity of the materials to absorb water (swelling indices of 1678% and 1597% for the RM and FeSiMn hydrogels, respectively) compared to the conventional polyacrylamide hydrogel (1119%). An improvement in Vickers microhardness and storage modulus (G') was also observed: the hybrid with 10% RM presented a G', 50 times higher than conventional hydrogel. The results show the merit of RM and FeSiMn in improving the properties of hydrogels.

Removal of hazardous ions from aqueous solutions: Current methods, with a focus on green ion flotation

Hazardous ions, like those of heavy metals, cause significant health and environmental problems when they are discharged into water resources naturally or through various industrial processes. Removing these ions from water is of significant importance in the provision of high-quality water for drinking and agricultural usage. This work discusses current techniques that are frequently used for the removal of heavy-metal ions from aqueous solutions by absorption, particularly the use of biodegradable surfactants in ion flotation. Certain new surfactants promise high efficiency in their use in the ion-flotation process and in their application in industrial-water treatment to remove heavy metals. As an example, this work demonstrates the high efficiency of surfactants based on an amino-acid (L-cysteine) in removing a range of heavy-metal ions in a simple, single-stage ion-flotation process. High foaming ability, the ability to operate in various temperatures and pHs, decomposing into natural products and high binding affinity for heavy-metal ions make the cysteine-based surfactants a highly suitable compound to replace current commercial surfactants in ion- and froth-flotation processes. Removal of particular ions can also be achieved in ion flotation; a suitable choice of parameters, such as pH and surfactant concentration, favours the surfactant binding to those ions. Further intensive work is required to develop an optimal process to recover valuable elements from waste solutions.

Preparation of new modified silica gel terminated with phenylphosphonic acid-amide moieties for adsorption of uranium(VI) from aqueous solutions

PAMAM dendrimers modified silica gel terminated phenylphosphonic acid-amide moieties (Si-6G PAMAM-PPAAM) was prepared for uranium(VI) adsorption from aqueous solutions by batch and fixed-bed column methods. The experimental results showed that the maximum capacity was 434.78 mg g−1. Equilibrium isotherm data obeyed Langmuir isotherm model. Kinetic adsorption followed pseudo-second order model and thermodynamic parameters implied the adsorption was spontaneous, endothermic. The adsorption performance of the new adsorbent toward uranium using fixed-bed column method was also investigated. The investigated adsorbent (Si-6G PAMAM-PPAAM) was successfully used to extract uranium from leach liquor of granitic rock sample.

Research progress and applications of silica-based aerogels - a bibliometric analysis

Silica aerogels are three-dimensional porous materials that were initially produced in 1931. During the past nearly 90 years, silica aerogels have been applied extensively in many fields. In order to grasp the progress of silica-based aerogels, we utilize bibliometrics and visualization methods to analyze the research hotspots and the application of this important field. Firstly, we collect all the publications on silica-based aerogels and then analyze their research trends and performances by a bibliometric method regarding publication year/citation, country/institute, journals, and keywords. Following this, the major research hotspots of this area with a focus on synthesis, mechanical property regulation, and the applications for thermal insulation, adsorption, and Cherenkov detector radiators are identified and reviewed. Finally, current challenges and directions in the future regarding silica-based aerogels are also proposed.

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.

Silica particles with fluorescein-labelled cores for evaluating accessibility through fluorescence quenching by copper

Core-shell particles with fluorescent cores were synthesised by growing silica shells on fluorescein-labelled Stöber-type particles. The porosity of the shell could be altered in a subsequent pseudomorphic transformation step, without affecting the particle size and shape. These core-shell particles constitute a platform for the evaluation of pore connectivity and core accessibility by observing the effect of a quencher on the fluorescence signal emitted by the fluorescein-labelled cores. In combination with argon sorption measurements, quenching experiments with copper provided valuable information on the porosity generated during the shell formation process. It was further observed that the introduction of well-defined mesopores by pseudomorphic transformation in the presence of a structure-directing agent reduces the core accessibility. This led to the conclusion that the analysis by conventional gas sorption methods paints an incomplete picture of the mesoporous structure, in particular with regard to pores that do not offer an unobstructed path from the external particle surface to the core.

A New Perspective on Adsorbent Materials Based Impregnated MgSiO3 with Crown Ethers for Palladium Recovery

The study of new useful, efficient and selective structures for the palladium ions’ recovery has led to the development of a new series of macromolecules. Thus, this study presents a comparative behavior of two crown benzene ethers that modify the magnesium silicate surface used as adsorbent for palladium. These crown ethers are dibenzo18-crown-6 (DB18C6) and dibenzo 30-crown-10 (DB30C10). The obtained materials were characterized by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX) and Fourier-transform infrared spectroscopy (FT-IR). The specific surface area (BET) and point of zero charge (PZC) of the two materials were determined. The palladium ions’ recovery from synthetic aqueous solutions studies aimed to establish the adsorption mechanism. For this desideratum, the kinetic, equilibrium and thermodynamic studies show that MgSiO₃-DB30C10 have a higher adsorption capacity (35.68 mg g⁻¹) compared to MgSiO₃-DB18C6 (21.65 mg g⁻¹). Thermodynamic studies highlight that the adsorption of Pd(II) on the two studied materials are spontaneous and endothermic processes. The positive values of the entropy (ΔS⁰) suggest that the studied adsorption processes show a higher disorder at the liquid/solid interface. Desorption studies were also performed, and it was found that the degree of desorption was 98.3%.

Towards a rational design of materials for the removal of environmentally relevant cations: polymer inclusion membranes (PIMs) and surface-modified PIMs for Sn2+ sequestration in aqueous solution

This work is focused on the design and preparation of polymer inclusion membranes (PIMs) for potential applications for stannous cation sequestration from water. For this purpose, the membranes have been synthesized employing two polymeric matrices, namely, polyvinylchloride (PVC) and cellulose triacetate (CTA), properly enriched with different plasticizers. The novelty here proposed relies on the modification of the cited PIMs by selected extractants expected to interact with the target cation in the membrane bulk or onto its surface, as well as in the evaluation of their performances in the sequestration of tin(II) in solution through chemometric tools. The composition of both the membrane and the solution for each trial was selected by means of a D-Optimal Experimental Design. The samples such prepared were characterized by means of TG-DTA, DSC, and static contact angles investigations; their mechanical properties were studied in terms of tensile strength and elastic modulus, whereas their morphology was checked by SEM. The sequestering ability of the PIMs toward stannous cation was studied by means of kinetic and isotherm experiments using DP-ASV. The presence of tin in the membranes after the sequestration tests was ascertained by μ-ED-XRF mapping on selected samples.

Preparation of Colored Microcapsule Phase Change Materials with Colored SiO2 Shell for Thermal Energy Storage and Their Application in Latex Paint Coating

This article reports the design and manufacture of colored microcapsules with specific functions and their application in architectural interior wall coating. Utilizing reactive dyes grafted SiO₂ shell to encapsulate paraffin through interfacial polymerization and chemical grafting methods, this experiment successfully synthesized paraffin@SiO₂ colored microcapsules. The observations of surface morphology demonstrated that the colored microcapsules had a regular spherical morphology and a well-defined core-shell structure. The analysis of XRD and FT-IR confirmed the presence of amorphous SiO₂ shell and the grafting reactive dyes, and the paraffin possessed high crystallinity. Compared with pristine paraffin, the thermal conductivity of paraffin@SiO₂ colored microcapsules was significantly enhanced. The results of DSC revealed that the paraffin@SiO₂ colored microcapsules performed high encapsulation efficiency and desirable latent heat storage capability. Besides, the examinations of UV-vis and TGA showed that the paraffin@SiO₂ colored microcapsules exhibited good thermal reliability, thermal stability, and UV protection property. The analysis of infrared imaging indicated that the prepared latex paint exhibited remarkable temperature-regulated property. Compared with normal interior wall coatings, the temperature was reduced by about 2.5 °C. With such incomparable features, the paraffin@SiO₂ colored microcapsules not only appeared well in their solar thermal energy storage and temperature-regulated property, but also make the colored latex paint coating have superb colored fixing capabilities.

Development of a reusable fluorescent nanosensor based on rhodamine B immobilized in Stöber silica for copper ion detection

This work has the goal of developing and evaluating a reusable fluorescent nanosensor for detection of Cu(ii) ion in aqueous solution, based on the immobilization of rhodamine B in silica nanoparticles prepared according to a modified Stöber method. In order to do this, a standard ammonium hydroxide ethanolic solution was mixed to ethanol under constant stirring, followed by the addition of tetraethoxysilane (TEOS). To immobilize the fluorescent reagent in the silica nanoparticles, rhodamine B ethanolic solution was added to the reacting mixture at different times (2; 3; 4 and 5 h) after starting the synthesis (which always lasts 7 h). The nanosensor obtained with the addition of rhodamine B after 5 h of synthesis showed the best sensitivity, measured as the fluorescence quenching, which was proportional to Cu(ii) ion. The nanosensor was selective to Cu(ii) ions and showed a linear range from 2.0 to 12.0 μmol L^-1, detection limit of 0.40 μmol L^-1, quantification limit of 1.3 μmol L^-1, response time of 50 s, being possible to be reused 3 times. The nanosensor was applied to the determination of Cu(ii) in sugar cane spirit and the results obtained did not show significant differences from those obtained by atomic absorption spectrometry at a confidence level of 95%.

Amino acid-functionalized carbon quantum dots for selective detection of Al3+ ions and fluorescence imaging in living cells

Carbon quantum dots (CQDs) are drawing tremendous attention due to their unique photoluminescence property and fascinating functions. Herein, we prepared novel CQDs functionalized with amino acids (AA-CQDs) by a one-pot hydrothermal method for selective detection of Al³⁺ ions and fluorescence imaging. The prepared AA-CQDs exhibit a novel triple-excitation and single-colour emission for fluorescent property. In addition, the AA-CQDs have a high absolute quantum yield (24.23%) and quantum lifetime (13.29 ns). Moreover, the AA-CQDs exhibit high selectivity and sensitivity for Al³⁺ by fluorescence enhancement. In pH 7.4 PBS solution, there was a good linear relation between the fluorescence intensity and the concentration of Al³⁺ in the range of 1-20 μmol L^-1; the limit of detection (3σ) was only 0.32 μmol L^-1. Furthermore, an AA-CQD probe was also utilized for detection of Al³⁺ in living cells based on excellent biocompatibility and endocytosis. Based on the concentration of Al³⁺ ions in cells and apoptosis data, there will be a quick reflect of apoptosis induced by aluminium ions via the fluorescence intensity of the AA-CQD probe. This work will set the stage for developing novel CQD-based biosensors in cell research.

Gas Phase Modification of Silica Nanoparticles in a Fluidized Bed: Tailored Deposition of Aminopropylsiloxane

Functionalized nanoparticles have various applications, for which grafting of a chemical moiety onto the surface to induce/improve certain properties is needed. When incorporated in polymeric matrices, for instance, the modified nanoparticles can alter the interfacial characteristics leading to improvements ofthe macroscopic properties of the nanocomposites. The extent of these improvements is highly dependent on the thickness, morphology and conformity of the grafted layer. However, the common liquid-phase modification methods provide limited control over these factors. A novel gas-phase modification process was utilized, with 3-aminopropyltriethoxysilane (APTES) as precursor, to chemically deposit amino-terminated organic layers on fumed silica nanoparticles in a fluidized bed. A self-limiting surface saturation was achieved when the reaction was done at 200 °C. With this self-limiting feature, we were able to graft multiple layers of aminopropylsiloxane (APS) onto the silica nanoparticles using water as the coreactant. The feasibility of this process was analyzed using thermogravimetric analysis (TGA), diffuse reflectance IR Fourier transform spectroscopy (DRIFTS), X-ray photoelectron spectroscopy (XPS), and elemental analysis (EA). By altering the number of APTES/water cycles, it was possible to control the thickness and conformity of the deposited aminopropylsiloxane layer. This novel approach allows to engineer the surface of nanoparticles, by introducing versatile functionalized layers in a controlled manner.

Controlled release evaluation of paracetamol loaded amine functionalized mesoporous silica KCC1 compared to microcrystalline cellulose based tablets

In the pharmaceutical manufacturing, drug release behavior development is remained as one of the main challenges to improve the drug effectiveness. Recently, more focus has been done on using mesoporous silica materials as drug carriers for prolonged and superior control of drug release in human body. In this study, release behavior of paracetamol is developed using drug-loaded KCC-1-NH2 mesoporous silica, based on direct compaction method for preparation of tablets. The purpose of this study is to investigate the utilizing of pure KCC-1 mesoporous silica (KCC-1) and amino functionalized KCC-1 (KCC-1-NH2) as drug carriers in oral solid dosage formulations compared to common excipient, microcrystalline cellulose (MCC), to improve the control of drug release rate by manipulating surface chemistry of the carrier. Different formulations of KCC-1 and KCC-NH2 are designed to investigate the effect of functionalized mesoporous silica as carrier on drug controlled-release rate. The results displayed the remarkable effect of KCC-1-NH2 on drug controlled-release in comparison with the formulation containing pure KCC-1 and formulation including MCC as reference materials. The pure KCC-1 and KCC-1-NH2 are characterized using different evaluation methods such as FTIR, SEM, TEM and N2 adsorption analysis.

Platinum (IV) Recovery from Waste Solutions by Adsorption onto Dibenzo-30-crown-10 Ether Immobilized on Amberlite XAD7 Resin-Factorial Design Analysis

Platinum is a precious metal with many applications, such as: catalytic converters, laboratory equipment, electrical contacts and electrodes, digital thermometers, dentistry, and jewellery. Due to its broad usage, it is essential to recover it from waste solutions resulted out of different technological processes in which it is used. Over the years, several recovery techniques were developed, adsorption being one of the simplest, effective and economical method used for platinum recovery. In the present paper a new adsorbent material (XAD7-DB30C10) for Pt (IV) recovery was used. Produced adsorbent material was characterized by X-ray dispersion (EDX), scanning electron microscopy (SEM) analysis, Fourier Transform Infrared Spectroscopy and Brunauer-Emmett-Teller (BET) surface area analysis. Adsorption isotherms, kinetic models, thermodynamic parameters and adsorption mechanism are presented in this paper. Experimental data were fitted using three non-linear adsorption isotherms: Langmuir, Freundlich and Sips, being better fitted by Sips adsorption isotherm. Obtained kinetic data were correlated well with the pseudo-second-order kinetic model, indicating that the chemical sorption was the rate-limiting step. Thermodynamic parameters (ΔG°, ΔH°, ΔS°) showed that the adsorption process was endothermic and spontaneous. After adsorption, metallic platinum was recovered from the exhausted adsorbent material by thermal treatment. Adsorption process optimisation by design of experiments was also performed, using as input obtained experimental data, and taking into account that initial platinum concentration and contact time have a significant effect on the adsorption capacity. From the optimisation process, it has been found that the maximum adsorption capacity is obtained at the maximum variation domains of the factors. By optimizing the process, a maximum adsorption capacity of 15.03 mg g⁻¹ was achieved at a contact time of 190 min, initial concentration of 141.06 mg L⁻¹ and the temperature of 45 °C.

Removal of Chromium(VI) by Chitosan Beads Modified with Sodium Dodecyl Sulfate (SDS)

In this study, chitosan beads modified with sodium dodecyl sulfate (SDS) were successfully synthesized and employed for the removal of chromium(VI) (Cr(VI)). The adsorption performance of the adsorbent (SDS-chitosan beads) was examined by batch experiments. The partition coefficient (PC) as well as the adsorption capacity were evaluated to assess the true performance of the adsorbent in this work. The adsorbent (SDS-chitosan beads) showed a maximum Cr(VI) adsorption capacity of 3.23 mg·g−1 and PC of 9.5 mg·g−1·mM−1 for Cr(VI). The prepared adsorbent was characterized by different techniques such as scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS) and Fourier transform-infrared spectroscopy (FT-IR). We used inductively coupled plasma mass spectrometry (ICP-MS) for the determination of Cr(VI) in solution. The experimental data could be well-fitted by pseudo-second-order kinetic and Langmuir isotherm models. The thermodynamic studies indicated that the adsorption process was favorable under the higher temperature condition. The SDS-modified chitosan beads synthesized in this work represent a promising adsorbent for removing Cr(VI).

Hollow Silica Cubes with Customizable Porosity

Hollow silica cubes were synthesized by a deposition of a thin silica shell onto micrometer-sized hematite cubes. Ordered mesopores with well-defined pore diameters of 2.8 nm and 3.8 nm were introduced into the silica shell by means of pseudomorphic transformation after removal of the hematite core. The particles retained their cubic morphology upon pseudomorphic transformation, allowing for the preparation of close-packed layers of the hollow mesoporous silica cubes by drop-casting and the visualization of the hollow core by focused ion beam scanning electron microscopy.