Aluminum Montmorillonite/Polyaniline Hybrid Composite-Based Organogels for the Expurgation of Carcinogenic Chlorophenols and Congo Red Dye from Defiled Water Sources

Chlorophenol and Congo Red dye being highly toxic are well known for their carcinogenic activity. This work focuses on preparing an organogel for the removal of both chlorophenol and Congo Red. PAni molecules were grafted in situ between the layers of montmorillonite (MMT) to form a PAni/MMT composite, which was further modified to form a gel structure. The composite was thoroughly characterized by high-resolution X-ray diffraction (HR-XRD), Fourier transform infrared (FT-IR) analysis, Brunauer-Emmett-Teller (BET) analysis, and thermogravimetric analysis (TGA). The gel was further analyzed by scanning electron microscopy (SEM) and by studying the rheological properties. The resulting gel exhibited an impressive solvent uptake, with a maximum of 2084% (20 times) for chlorophenol, while the dye adsorption capacity was 349.72 mg/g with 99.44% removal efficiency. The adsorption proceeded with the pseudo-second-order model followed by the Langmuir monolayer adsorption model and Weber's intraparticle diffusion model. The sorbent was found to be selective among cationic dyes while retaining 83% of dye even in the fifth cycle. The hybrid sorbent shows great promise for sustainable purposes, and the results of this study are certainly encouraging.

Block Copolymer-Assisted Synthesis of Iron Oxide Nanoparticles for Effective Removal of Congo Red

Iron oxide nanoparticles (IONPs) were synthesized via a block copolymer-assisted hydrothermal method and the phase purity and the crystal structure were investigated by X-ray diffraction. The Rietveld analysis of X-ray diffractometer spectra shows the hexagonal phase symmetry of α-Fe₂O₃. Further, the vibrational study suggests Raman active modes: 2A1g + 5Eg associated with α-Fe₂O₃, which corroborates the Rietveld analysis and orbital analysis of 2PFe. The superparamagnetic behavior is confirmed by magnetic measurements performed by the physical properties measurement system. The systematic study of the Congo red (CR) interaction with IONPs using a UV-visible spectrophotometer and a liquid chromatography-tandem mass spectrometry system equipped with a triple quadrupole mass analyzer and an electrospray ionization interface shows effective adsorption. In visible light, the Fe₂O₃ nanoparticles get easily excited and generate electrons and holes. The photogenerated electrons reduce the Fe³⁺ ions to Fe²⁺ ions. The Fe²⁺/H₂O₂ oxidizes CR by the Fenton mechanism. The strong adsorption ability of prepared nanoparticles towards dyes attributes the potential candidates for wastewater treatment and other catalytic applications.

A Novel Metal-Containing Mesoporous Silica Composite for the Decolorization of Rhodamine B: Effect of Metal Content on Structure and Performance

A series of novel Mn_xFe_y@SiO₂ (x,y = 1-20%) nanocomposites were synthesized for the first time via the sol-gel/combustion method with different content of precursors (Mn and Fe acetate salts). The effect of precursor content and ratio on physicochemical properties were observed by various characterization methods. Moreover, Rhodamine B (RhB) was chosen as the target pollutant to test the performance of these nanocomposites under a photocatalytic Fenton-like reaction. The results showed that the nanocomposite morphology improved by increasing Fe and Mn content. In this study, interesting behavior was observed in BET results which were different from the fact that increasing metal content can decrease the surface area. This study revealed that one metal could be more critical in controlling the properties than another. Moreover, the precursor ratio appears to have a more tangible effect on the surface area than the effect of precursor content. Among all synthesized nanocomposites, Mn₁Fe₅@SiO₂ showed the highest surface area of 654.95 m²/g. At optimum batch conditions (temp = 25 °C, catalyst dosage = 1 g L^-1, H₂O₂ = 75 mmolL^-1, and initial RhB concentration = 50 mg L^-1), complete removal (simultaneous adsorption/degradation) occurred using Mn₁Fe₅@SiO₂ at neutral pH. This study showed that the designed nanomaterial could be used as a dual functional adsorbent/photocatalyst in different environmental applications.

Impact of preparation method on nickel speciation and methane dry reforming performance of Ni/SiO2 catalysts

The methane dry reforming reaction can simultaneously convert two greenhouse gases (CH₄ and CO₂), which has significantly environmental and economic benefits. Nickel-based catalysts have been widely used in methane dry reforming in past decade due to their low cost and high activity. However, the sintering and coke deposition of catalysts severely limit their industrial applications. In this paper, three Ni/SiO₂ catalysts prepared by different methods were systematically studied, and the samples obtained by the ammonia evaporation method exhibited excellent catalytic performance. The characterization results such as H₂-TPR, XPS and TEM confirmed that the excellent performance was mainly attributed to the catalyst with smaller Ni particles, stronger metal-support interactions, and abundant Ni-O-Si units on the catalyst surface. The anti-sintering/-coking properties of the catalyst were significantly improved. However, the Ni/SiO₂-IM catalyst prepared by impregnation method had uneven distribution of nickel species and large particles, and weak metal-support interactions, showing poor catalytic performance in methane dry reforming. Since the nickel species were encapsulated by the SiO₄ tetrahedral network, the Ni/SiO₂-SG catalyst prepared by sol-gel method could not expose more effective active sites even if the nickel species were uniformly dispersed, resulting in poor dry reforming performance. This study provides guidance for the preparation of novel anti-sintering/-coking nickel-based catalysts.

Metal-organic frameworks-derived hierarchical Co3O4/CoNi-layered double oxides nanocages with the enhanced catalytic activity for toluene oxidation

The development of active transition-metal oxide (TMO) catalysts for the abatement of volatile organic compounds (VOCs) remains a great challenge. Controllable synthesis of TMOs with specific morphology and suitable composition is a promising way for acquiring efficient oxidation catalysts. Herein, a series of hierarchical Co₃O₄/CoNi-layered double oxides (CoNi-LDO) nanocages covered by interlaced nanosheets were synthesized using a cobalt metal-organic framework (Co-MOF)-based strategy. The textural properties, morphology, surface chemical state, and reducibility of the CoNi-LDO catalysts were systematically characterized by various techniques. The catalytic activity toward toluene oxidation and the stability performance was investigated. Results demonstrated that the morphology, composition, and textual properties can be controlled by tuning the post-synthetic etching reaction conditions. Benefiting from the structural and compositional merits, as well as the superior low-temperature reducibility, the CoNi-LDO-1 catalyst (Ni/Co molar ratio was 0.39) with core-shell structure exhibited excellent activity toward toluene oxidation. Our work offers a new strategy for the design of high-performance oxidation catalysts for the abatement of VOCs.

Polypyrrole functionalized Cobalt oxide Graphene (COPYGO) nanocomposite for the efficient removal of dyes and heavy metal pollutants from aqueous effluents

A cobalt oxide graphene nanocomposite functionalized with polypyrrole (COPYGO) having a heterogenous porous structure was synthesized using hydrothermal method. Microscopic imaging of the COPYGO surface revealed its highly porous and ordered features. The adsorption performance of the COPYGO composite was systemically investigated for Methylene Blue (MB), Congo red (CR) dyes and toxic lead (Pb(II)) and Cadmium (Cd(II)) metals. These were selected as they are the common pollutants in industrial wastewater. The COPYGO was found to be thermally stable up to 195 ^oC with a specific surface area of 133 m² g^-1. Experimental data indicates that the COPYGO follows Langmuir and Temkin adsorption isotherm. The COPYGO was efficient in removing MB (92.8%), CR (92.2%), Pb(II) (93.08%) and Cd(II) (95.28%) pollutants at pH 7.2, 5.0, 5.5 and 6.1 respectively from the simulated effluents. The maximum adsorption capacity (Q_max) observed for MB 663.018 mg g^-1, CR 659.056 mg g^-1, Pb(II) 780.363 mg g^-1 and Cd(II) 794.188 mg g^-1 pollutants. The thermodynamic analysis of the COPYGO indicates that the adsorption is endothermic and spontaneous in nature. COPYGO showed very high efficient removal rate for the pollutants in simulated effluents which guaranteed its benefits and efficacy in industrial wastewater treatment.

Robust nickel silicate catalysts with high Ni loading for CO2 methanation

CO₂ is the main component of greenhouse gases and also an important carbon source. The hydrogenation of CO₂ to methane using Ni-based catalysts can not only alleviate CO₂ emissions but also obtain useful fuels. However, Ni-based catalysts face one major problem of the sintering of Ni nanoparticles in the process of CO₂ methanation. Thus, this work has synthesized a series of efficient and robust nickel silicate catalysts (NiPS-X) with different nickel content derived from nickel phyllosilicate by the hydrothermal method. It was found that the Ni loading plays a critical role in the structure and catalytic performance of the NiPS-X catalysts. The catalytic performance gradually increases with the increase of Ni loading. In particular, the highly dispersed NiPS-1.6 catalyst with a high Ni loading of 34.3 wt% could obtain the CO₂ conversion greater than 80%, and the methane selectivity was close to 100% for 48 h at 330 °C and the GHSV of 40,000 mL g^-1  h^-1 . The excellent catalytic property can be assigned to the high dispersion of Ni nanoparticles and the strong interaction between the active component and the carrier, which is derived from a unique layered silicate structure with lots of nickel phyllosilicate and a large number of Lewis acid sites.

Review on nickel-based adsorption materials for Congo red

Excessive synthetic dyestuffs in the aquatic environment pose various ecological and health issues that are detrimental to sustainable development. Adsorption is considered a feasible technique of eliminating dye pollutants from the water environment because of its advantages of high efficiency, low cost, easy operation, and absence of secondary pollution. Among the many dyes, Congo red (CR) is a widely used azo dye. Nickel-based materials, including nickel hydroxide, nickel oxide, nickel-containing layered double hydroxides, nickel-based spinel and metal-organic frameworks, metallic nickel, nickel-based sulfide, and nickel composites, have been extensively studied for CR adsorption due to their morphological diversity, large specific surface area, and strong affinity toward CR. However, fabricating nickel-based adsorbents with high efficiency and stability and excellent recyclability for practical application remains a challenge. This review outlines the research progress of nickel-based materials in CR adsorption. The interaction between CR molecules and nickel-based adsorbents is systematically presented, and the possible adsorption mechanisms are summarized. Finally, the challenges and future development directions of the practical application of nickel-based adsorbent materials are proposed.

Instantaneous Adsorption of Synthetic Dyes from an Aqueous Environment Using Kaolinite Nanotubes: Equilibrium and Thermodynamic Studies

Innovative kaolinite nanotubes (KNTs) are synthesized utilizing a simple technique involving a sonication-induced exfoliation process, followed by chemical scrolling reactions. The KNTs as a material have high reactivity and promising surface area to be used in the purification of water from cationic dyes (safranin (SF) and malachite green (MG)) and anionic dyes (methyl orange (MO) and Congo red (CR)). The kinetic studies of the four dyes SF, MG, CR, and MO show an equilibration time interval of 240 min. The SF, MG, CR, and MO dyes' uptake reactions are in agreement with the kinetic behavior of the pseudo-first-order model and the equilibrium properties of the Langmuir model. Such modeling results, in addition to the Gaussian energies from the Dubinin-Radushkevich (D-R) model (SF (1.01 kJ/mol), MG (1.08 kJ/mol), CR (1.11 kJ/mol), and MO (1.65 kJ/mol)), hypothesize monolayer adsorption of the four dyes by physical reactions. The KNTs show theoretical q _max values of 431.6, 489.9, 626.2, and 675.5 (mg/g) for SF, MG, CR, and MO, respectively. The thermodynamic examination of SF, MG, CR, and MO adsorption reactions using KNTs verifies their adsorption by exothermic and spontaneous reactions. The KNT adsorbents achieve promising adsorption results in the presence of different coexisting ions and show significant recyclability properties. Therefore, the production of KNTs from kaolinite shows a strong effect on inducing the textural, physicochemical, and adsorption properties of clay layers as well as their affinity for different species of synthetic dyes.

Nickel-Aluminum Oxide Aerogels: Super-adsorbents for Azo Dyes for Water Remediation

Highly porous nickel-aluminum oxide aerogels were prepared according to a one-pot sol-gel process and dried under supercritical carbon dioxide conditions. Although the surface properties of these materials were very appealing for applications in catalysis, these aerogels were never applied in adsorption. The nickel effect on the structure and surface properties of the aerogels has been investigated via a broad range of structural, textural, and morphology characterization of the aerogels before and after heat treatment. The adsorption capacity of the as-synthesized and calcined aerogels for azo dyes was assessed under various experimental conditions. The presence of nickel in the aerogel boosts tremendously the surface reactivity and improves noticeably the adsorption capacity of the material. The adsorption capacities for the nickel-aluminum oxide aerogel with 40% nickel (q max) are 900 mg g-1 for methyl orange, 1484 mg g-1 for orange II, and 1660 mg g-1 for Congo Red. The adsorption process is exothermic and follows pseudo-second-order kinetics.

Brief bibliometric analysis of "ionic liquid" applications and its review as a substitute for common adsorbent modifier for the adsorption of organic pollutants

The importance of improving adsorbent's adsorption efficiency in organic pollutants has been reported by many researchers. Surfactant-based modified adsorbents were a tasteful choice. As a result, the use of surfactants as a modifier for removing organic pollutants has shown to play a very big role in enhancing the adsorption efficiency of different materials. Ionic liquids are receiving extensive interest as green multipurpose compounds, primarily as a replacement for traditional chemicals that are used in many chemical processes. This work gives a brief bibliometric analysis of application of ionic liquid from 1930 to 2017, documents were collected from Scopus database and keywords from the abstracts and titles were analyzed using VOSviewer software. Furthermore, the work presents a review of conventionally known surfactants and the recent likelihood of ionic liquids for modifying adsorbents for adsorption of organic pollutants. Over the period of years between 1930 and 2017, 13,144 documents were published on the application of ionic liquids. VOSviewer software further confirms that adsorption is one of the leading areas in applications of ionic liquids. Review also showed that ionic liquid is a good modifier of adsorbents.

3D hierarchical graphene oxide-NiFe LDH composite with enhanced adsorption affinity to Congo red, methyl orange and Cr(VI) ions

Three-dimensional (3D) hierarchical graphene oxide-NiFe layered double hydroxide (GO-NiFe LDH) composite with sandwich-like structure is fabricated using a facile one-pot hydrothermal reaction. Electron microscopy images demonstrate that the GO-NiFe LDH composite possesses a highly porous and well-ordered structure. Both sides of the GO are fully covered by the LDH nanosheets, resulting in the sandwich-like architecture. The adsorption performance of the GO-NiFe LDH composite and pure NiFe LDH for three anionic pollutants, namely, Congo red (CR), methyl orange (MO) and hexavalent chromium ion [Cr(VI)] is systematically investigated. The presence of GO in the GO-NiFe LDH composite leads to the better adsorption capability and faster adsorption kinetics of this composite compared with the NiFe LDH microspheres. The pseudo-second-order kinetic model can well represent the adsorption kinetics, and the Langmuir isotherm model provides a better description for the adsorption isotherms. The GO-NiFe LDH composite demonstrates appreciable potential in alleviating anionic pollutants from the aquatic environment as shown by its excellent adsorption capability towards CR, MO and Cr(VI).

Cotton fiber-supported layered double hydroxides for the highly efficient adsorption of anionic organic pollutants in water

Cotton fiber is used as a substrate for the immobilization of LDHs and applied for the adsorption anionic pharmaceuticals and dyes.

Template-free synthesis of nanoparticle-built MgO and Zn-doped MgO hollow microspheres with superior performance for Congo red adsorption from water

A template-free route was developed to synthesize MgO and Zn-doped MgO hollow microspheres with ultrahigh adsorption performances and excellent reusability.

Magnetic mesoporous TiO2 microspheres for sustainable arsenate removal from acidic environments

Unique magnetic mesoporous TiO₂ microspheres exhibit superior arsenate removal performance and high stability in acidic environments.

Hierarchically porous SiO2/C hollow microspheres: a highly efficient adsorbent for Congo Red removal

Hierarchically porous SiO₂/C hollow microspheres (HPSCHMs) were synthesized by a hydrothermal and NaOH-etching combined route. The adsorption performance of the prepared HPSCHMs was investigated to remove Congo Red (CR) in aqueous solution. The results show that the synthesized composite possesses a hollow microspherical structure with hierarchical pores and a diameter of about 100–200 nm, and its surface area is up to 1154 m² g⁻¹. This material exhibits a remarkable adsorption performance for CR in solution, and its maximum adsorption amount for CR can reach up to 2512 mg g⁻¹. It shows faster adsorption and much higher adsorption capacity than the commercial AC and γ-Al₂O₃ samples under the same conditions. The studies of the kinetics and thermodynamics indicate that the adsorption of CR on the PHSCHM sample obeys the pseudo-second order model well and belongs to physisorption. The adsorption activation energy is about 7.72 kJ mol⁻¹. In view of the hierarchically meso–macroporous structure, large surface area and pore volume, the HPSCHM material could be a promising adsorbent for removal of pollutants, and it could also be used as a catalyst support.

Hierarchically porous SiO₂/C hollow microspheres (HPSCHMs) were synthesized. Its surface area is up to 1154 m² g^–1. Hierarchically porous structure facilitates diffusion of adsorbate. Its maximum adsorption amount for Congo Red is up to 2512 mg g^–1.

Hierarchical Porous Magnesium Oxide (Hr-MgO) Microspheres for Adsorption of an Organophosphate Pesticide: Kinetics, Isotherm, Thermodynamics, and DFT Studies

In this study, hierarchical porous magnesium oxide (Hr-MgO) microspheres have been fabricated from a hydromagnesite precursor via a facile precipitation method followed by calcination. The Hr-MgO microspheres consist of several nanosheet building blocks that generate a flowerlike architecture. Chlorpyrifos (CPF), a persistent organic pollutant, has been chosen as a model organophosphate pesticide to determine the adsorptive capacities of the fabricated Hr-MgO. The equilibrium adsorption data fits well with the Langmuir isotherm model, showing a maximum adsorption capacity of 3974 mg g^-1, which is the highest value to date. Both kinetic as well as thermodynamic parameters reveal the spontaneous, exothermic, and pseudo-second-order nature of the adsorption process due to chemisorption between the pesticide and the adsorbent. Density functional theory studies suggest the importance of hydroxylation on the MgO surface for the successful destructive adsorption, which takes place via the cleavage of S═P and Cl-C bonds resulting in the fragmentation of CPF, which is in good agreement with Fourier transform infrared and mass spectrometric studies. The present study shows the potential use of hierarchically structured porous MgO microspheres as an efficient adsorbent for the removal of CPF pollutant.

One-Step Fabrication of Fe(OH)3@Cellulose Hollow Nanofibers with Superior Capability for Water Purification

The conventional strategies employed for the synthesis of hollow nanofibers (HNFs) require either multistep treatments or special design of the equipment. An additional annealing process is always required, which inevitably consumes more energy and raises the manufacturing cost. In addition, the annealing process may also cause a waste of the matrix materials and the release of toxic gases. Herein, we report for the first time a novel one-step synthesis of hollow hybrid nanofibers via electrospinning. Cellulose was chosen as the polymer matrix, and Fe(OH)₃ nanoparticles were grown in situ on the nanofibers during electrospinning. There was no need to remove cellulose to create the hollow nanofiber structure. This can significantly simplify the fabrication process without any negative influence to the air. The obtained Fe(OH)₃@cellulose HNF membranes exhibited great mechanical properties and an extremely high water flux of 11 200 L m^-2 h^-1 bar^-1. They could effectively remove various pollutants in water, including phosphate, heavy metal ions, and organic dyes, with excellent reusability. Importantly, this approach could also be applied for the fabrication of other hybrid HNFs, which may serve in a broad range of scientific and engineering applications, including water purification, energy conversion and storage, catalysts, sensors, and so on.

Superb adsorption capacity of hierarchical calcined Ni/Mg/Al layered double hydroxides for Congo red and Cr(VI) ions

The preparation of hierarchical porous materials as catalysts and sorbents has attracted much attention in the field of environmental pollution control. Herein, Ni/Mg/Al layered double hydroxides (NMA-LDHs) hierarchical flower-like hollow microspheres were synthesized by a hydrothermal method. After the NMA-LDHs was calcined at 600°C, NMA-LDHs transformed into Ni/Mg/Al layered double oxides (NMA-LDOs), which maintained the hierarchical flower-like hollow structure. The crystal phase, morphology, and microstructure of the as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy elemental mapping, Fourier transform infrared spectroscopy, and nitrogen adsorption-desorption methods. Both the calcined and non-calcined NMA-LDHs were examined for their performance to remove Congo red (CR) and hexavalent chromium (Cr(VI)) ions in aqueous solution. The maximum monolayer adsorption capacities of CR and Cr(VI) ions over the NMA-LDOs sample were 1250 and 103.4mg/g at 30°C, respectively. Thermodynamic studies indicated that the adsorption process was endothermic in nature. In addition, the addition of coexisting anions negatively influenced the adsorption capacity of Cr(VI) ions, in the following order: CO₃^2->SO₄^2->H₂PO₄^->Cl^-. This work will provide new insight into the design and fabrication of advanced adsorption materials for water pollutant removal.

A facile sacrificial template method to synthesize one-dimensional porous CdO/CdFe2O4 hybrid nanoneedles with superior adsorption performance

A novel adsorbent based on 1D porous CdO/CdFe₂O₄ hybrid nanoneedles has been firstly synthesized via a facile sacrificial template (solid Cd₂Fe(CN)₆) method, which exhibit an superior adsorption capacity of 1491 mg g⁻¹ for CR from aqueous solution.

Adsorption–reduction of chromium(vi) from aqueous solution by phenol–formaldehyde resin microspheres

A novel adsorbent of phenol–formaldehyde resin (PF) microspheres was prepared at a low temperature, and had an excellent performance for the adsorption–reduction of Cr(vi).

Effect of calcination on adsorption performance of Mg–Al layered double hydroxide prepared by a water-in-oil microemulsion method

Calcined Mg–Al layered double hydroxides synthesized by water-in-oil microemulsion method exhibit an enhanced adsorption performance for orange II.

Adsorption properties of ZrO2 hollow microboxes prepared using CaCO3 cubes as templates

ZrO₂ hollow microboxes prepared using CaCO₃ cube as template exhibit excellent dye adsorption performance from wastewater.

Cauliflower-like Ni/NiO and NiO architectures transformed from nickel alkoxide and their excellent removal of Congo red and Cr(vi) ions from water

Cauliflower-like nickel alkoxide, Ni/NiO and NiO architectures were synthesized via a reflux route using NaBH₄–EG as alkaline precipitant.