A facile hydrothermal synthesis, adsorption kinetics and isotherms to Congo Red azo-dye from aqueous solution of NiO/graphene nanosheets adsorbent

Unveiling the remarkable simultaneous adsorption-photocatalytic potential of Ag nanoparticles-anchored phosphotungestic acid loaded ZIF-8 for Congo red removal

This research paper presents a direct approach to synthesize AgNPs deposited on polyoxometalate/ZIF-8 on-site (referred to as AgNPS@PW@ZIF-8) to develop a highly efficient photocatalyst in the water treatment. Phosphotungestic acid (PW) serves a multi-purpose in this context: it acts as a bridge layer between AgNPs and Zeolitic Imidazolate Framework-8 (ZIF-8), a local reducing agent, and a catalyst for electron transfer during the photocatalysis process. A comprehensive characterization of the resulting nanostructure was performed utilizing an array of techniques, such as XRD, FTIR, EDX, TEM, BET, Raman, and TGA. The nanostructure that was created exhibited effective removal of Congo red at different pH levels via a combination of simultaneous adsorption and photocatalysis. After 60 min at pH 7, the dye molecules were completely eliminated in the presence of 0.5 g/L AgNPS@PW@ZIF-8 at room temperature. The charge transfer can be facilitated by the PW bridge layer connecting AgNPs and ZIF-8, owing to the photoactive characteristics and strong electron transfer capabilities of PW molecules. Strong electron transferability of PW between Ag nanoparticles and ZIF-8 facilitates charge transfer and significantly improves the photocatalytic performance of ZIF-8. Moreover, the nanostructure demonstrated great structural stability and recyclability, sustaining a high efficiency of removal throughout five consecutive cycles through the implementation of a simple procedure. Widespread applications of the developed nanostructure in aquatic environments for adsorption and photocatalytic reactions are possible.

Salsola Tetragona as a new low-cost adsorbent for water treatment: highly effective adsorption of crystal violet

Synthetic dyes are prevalent in aquatic environments, they have high toxicities, are non-degradable, and accumulate in the water. The removal of Crystal violet (CV) is carried out using batch experiments on the Salsola Tetragona (ST) plant as a novel adsorbent. The prepared adsorbent was analyzed by various methods (MEB, EDX, IRTF and PZC), to support its applicability as adsorbent. The adsorption study of CV is performed by optimizing the parameters affecting the adsorption process. The adsorption kinetics study is represented by pseudo-second-order (R2 = 0.999) and the adsorption process is limited by external mass transport. In addition, the isotherm results demonstrate that the Langmuir model interprets better the adsorption isotherm. The thermodynamic parameters suggest that the adsorption phenomena are spontaneous and exothermic. Furthermore, the adsorption reactions involved are of physisorption type, which facilitates the desorption of pollutants from the surface of the adsorbent. The results show that ST adsorbent effectively removes CV in an aqueous solution, which is demonstrated by the maximum amount adsorption of 246.7 mg.g-1 at optimum adsorption conditions: pH = 6, adsorbent dose of 0.5 g.L-1, initial CV concentration of 10 mg.L-1, and adsorption time of 30 min at 298 K. Finally, these results can be considered as a useful reference for wastewater treatment using ST.

Improvement of Supercapacitor Performance of In Situ Doped Laser-Induced Multilayer Graphene via NiO

Herein, we have reported a novel strategy for improving the electrochemical performance of laser-induced graphene (LIG) supercapacitors (SCs). The LIG was prepared using a CO₂ laser system. The polyimide polymer was the source material for the fabrication of the LIG. The doping process was performed in situ using the CO₂ laser, which works as a rapid thermal treatment to combine graphene and NiO particles. NiO was used to improve the capacitance of graphene by combining an electric double-layer capacitor (EDLC) with the pseudo-capacitance effect. The high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, and Raman spectroscopy showed that the structure of the LIG is multilayered and waved. The HRTEM image proves the distribution of NiO fine particles with sizes of 5-10 nm into the graphene layers. The electrochemical performance of the as-prepared LIG was tested. The effect of the combination of the two materials (oxide and carbon) was investigated at different concentrations. The LIG showed a specific capacitance of 69 Fg^-1, which increased up to 174 Fg^-1 for the NiO-doped LIG. The stability investigations showed that the electrodes were very stable for more than 1000 cycles. This current study establishes an innovative method to improve the electrochemical properties of LIG.

Exploration of Reactive Black 5 Dye Desorption from Composite Hydrogel Beads—Adsorbent Reusability, Kinetic and Equilibrium Isotherms

A low-cost adsorbent was prepared by using cherry stones powder and chitosan and used to retain Reactive Black 5 dye from aqueous solution. Then, the spent material was submitted to a regeneration process. Five different eluents (water, sodium hydroxide, hydrochloric acid, sodium chloride and ethanol) were tested. Among them, sodium hydroxide was selected for an advanced investigation. Values of three working conditions, namely the eluent volume, its concentration and the desorption temperature, were optimized by Response Surface Methodology-Box–Behnken Design. In the established settings (NaOH volume: 30 mL, NaOH concentration: 1.5 M, working temperature: 40 °C), three successive cycles of adsorption/desorption were conducted. The analysis performed by Scanning Electron Microscopy and by Fourier Transform Infrared Spectroscopy revealed the evolution of the adsorbent throughout the dye elution from the material. Pseudo-second-order kinetic model and Freundlich equilibrium isotherm were able to accurately describe the desorption process. Based on the acquired results, our outcomes sustain the suitability of the synthesized material as dye adsorbent and the possibility of efficaciously recycling and reusing it.

Performance of Dye Removal from Single and Binary Component Systems by Adsorption on Composite Hydrogel Beads Derived from Fruits Wastes Entrapped in Natural Polymeric Matrix

The treatment of contaminated water is currently a major concern worldwide. This work was directed towards the preparation of a composite hydrogel by entrapping cherry stones powder on chitosan, which is known as one of the most abundant natural polymers. The synthesized material was characterized by scanning electron microscopy, by Fourier transform infrared spectroscopy, and by the point of zero charge determination. Its ability to remove two azo dyes models (Acid Red 66 and Reactive Black 5) existing in single form and in binary mixture was evaluated. Response Surface Methodology-Central Composite Design was used to optimize three parameters affecting the process while targeting the lowest final contaminant concentrations. The best results were obtained at pH 2, an adsorbent dose of 100 g/L, and a temperature of 30 °C, when more than 90% of the pollutants from the single component systems and more than 70% of those of the binary mixtures were removed from their aqueous solutions. The adsorption process was in accordance with Elovich and pseudo-second-order kinetic models, and closely followed the Freundlich and Temkin equilibrium isotherms. The obtained results led to the conclusion that the prepared hydrogel composite possesses the ability to successfully retain the target molecules and that it can be considered as a viable adsorbent material.

Adsorption of anionic dyes from textile wastewater utilizing raw corncob

Toxic dyes are irrefutable effluent components of textile wastewater, so they have become a major economic and health concern. With the purpose of efficient removal of textile dyes, multiple nature-inspired adsorbents have been applied. Herein, raw corncob is proposed as a novel highly efficient, low-price, and abundantly attainable adsorbent with the potential for uptake of methyl red and methyl orange. Multiple experiments were carried out to optimize parameters including pH, primary concentration, adsorbent dosage, temperature, and contact time. The adsorption was raised with the mounting of the contact time and it was alleviated with the addition of initial concentration. The foremost uptake of dye was apperceived at an acidic medium pH 4 for methyl red and pH 1 for methyl orange. Scanning Electron Microscopy and Fourier Transform Infrared Spectroscopy were employed to characterize the surfaces of corncobs. The well-fitted Langmuir and Freundlich models (methyl red: R² = 0.9956 and methyl orange: R² = 0.9883) confirmed the homogeneous monolayer adsorption process on the raw corncob surface. The obtained results disclose that corncob is an effectual biosorbent for eliminating anionic dyes without the necessity for any prior modifications.

Manganese Molybdenum Oxide Micro Rods Adorned Porous Carbon Hybrid Electrocatalyst for Electrochemical Determination of Furazolidone in Environmental Fluids

The frequent occurrence of furazolidone (FZD) in environmental fluids reveals the ongoing increase in use and raises concerns about the need of monitoring it. To investigate the electrochemical behavior of FZD, a novel sensor of manganese molybdenum oxide (MMO) micro rods adorned three-dimensional porous carbon (PC) electrocatalyst was constructed. The crystalline structure and surface morphology of the MMO/PC composite was characterized by XRD, Raman, FESEM, and HR-TEM. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and amperometric(i-t) methods were used to assess the electrocatalytic activity of modified electrodes. In the presence of FZD, the as-fabricated MMO/PC modified glassy carbon electrode (GCE) performed better at lower potentials with a greater peak current than other modified GCE. These results emanate from the synergistic effect of the MMO/PC suspension on the GCE. The electrochemical behavior of the amperometric(i-t) technique was used to determine FZD. Amperometric(i-t) detection yielded linear dynamic ranges of 150 nM to 41.05 µM and 41.05 to 471.05 µM with detection limits of 30 nM. The MMO/PC hybrid sensor was also effectively used to detect FZD in environmental fluids, yielding ultra-trace level detection.

Synthesis of novel Co3O4 nanocubes-NiO octahedral hybrids for electrochemical energy storage supercapacitors

Fabrication of novel metal oxide nanostructured composites is a proficient approach to develop efficient energy storage devices and development of cost-free and eco-friendly metal oxide nanostructures for supercapacitor applications received considerable attention in recent years. The Co₃O₄ nanocubes-NiO octahedral structured composite was constructed using facile and one-step calcination process. Cyclic voltammetry, charge-discharge, and electrochemical impedance spectral techniques have been employed to analyze the specific capacitance of the synthesized nanostructures and the composites. Specific capacitance and cycling stability of the composites were evaluated with the pristine Co₃O₄ and NiO nanostructures. The composite showed a specific capacitance of 832 F g^-1 at a current density of 0.25 A g^-1, which was ~1.5 and ~1.9-times higher than pristine Co₃O₄ nanocubes and NiO octahedral structure, respectively. On the other hand, electrode showed approximately 50 % capacity retention at a higher current density (5 Ag^-1) because of the uniform morphology of Co₃O₄ and NiO. The charge-discharge stability measurements of the composite showed an admirable specific capacitance retention capability, which was 94.5 % after 2000 continuous charge-discharge cycles at a current density of 5 A g^-1. The superior electrochemical performance of the nano-composite was ascribed to synergistic effects and uniform morphology. Efficient nanostructure development using facile and one-step calcination process and electrochemical performance make the synthesized composite a promising device for supercapacitor applications.

Modern Carbon-Based Materials for Adsorptive Removal of Organic and Inorganic Pollutants from Water and Wastewater

Currently, a serious threat for living organisms and human life in particular, is water contamination with persistent organic and inorganic pollutants. To date, several techniques have been adopted to remove/treat organics and toxic contaminants. Adsorption is one of the most effective and economical methods for this purpose. Generally, porous materials are considered as appropriate adsorbents for water purification. Conventional adsorbents such as activated carbons have a limited possibility of surface modification (texture and functionality), and their adsorption capacity is difficult to control. Therefore, despite the significant progress achieved in the development of the systems for water remediation, there is still a need for novel adsorptive materials with tunable functional characteristics. This review addresses the new trends in the development of new adsorbent materials. Herein, modern carbon-based materials, such as graphene, oxidized carbon, carbon nanotubes, biomass-derived carbonaceous matrices-biochars as well as their composites with metal-organic frameworks (MOFs) and MOF-derived highly-ordered carbons are considered as advanced adsorbents for removal of hazardous organics from drinking water, process water, and leachate. The review is focused on the preparation and modification of these next-generation carbon-based adsorbents and analysis of their adsorption performance including possible adsorption mechanisms. Simultaneously, some weak points of modern carbon-based adsorbents are analyzed as well as the routes to conquer them. For instance, for removal of large quantities of pollutants, the combination of adsorption and other methods, like sedimentation may be recommended. A number of efficient strategies for further enhancing the adsorption performance of the carbon-based adsorbents, in particular, integrating approaches and further rational functionalization, including composing these adsorbents (of two or even three types) can be recommended. The cost reduction and efficient regeneration must also be in the focus of future research endeavors. The targeted optimization of the discussed carbon-based adsorbents associated with detailed studies of the adsorption process, especially, for multicomponent adsorbate solution, will pave a bright avenue for efficient water remediation.

Importance of Combined Electrochemical Process Sequence and Electrode Arrangements: A Lab-scale Trial of Real Reverse Osmosis Landfill Leachate Concentrate

Reverse osmosis (RO) is a widely applied technique for wastewater effluent reuse and landfill leachate treatment. The latter generates a refractory RO leachate concentrate (ROLC), for which cost-effective treatment is required. This study focuses on a two-step electrochemical method consisting of aluminum-based electrocoagulation (EC), and simultaneous electrooxidation-electrocoagulation with a titanium-based lead dioxide (Ti/ß-PbO₂) anode and aluminum cathode (EO_EC) assembly. The sequence and electrode arrangements of the combined electrochemical process were investigated to determine the organic transformation, Ti/ß-PbO₂ anode viability, and energy consumption. Series-based EC-EO_EC decreased the total chemical oxygen demand (COD) from 8750 mg L^-1 to 380 mg L^-1, a 96% removal efficiency, in 3.5 hours at 141 A m^-2. Under a low energy consumption of 28.7 kWh kg_COD^-1, the ROLC biodegradability (BOD₅/COD) significantly increased from 0.015 to 0.530, which was ascribed to aromatic removal (e.g., -C=C) and an increase in -COOH functional groups. Furthermore, the rapid removal of natural organic matter and increase in pH elevation from EC suppressed the dissolution of Pb from the Ti/ß-PbO₂ anode during the subsequent EO_EC, thereby leaving 0.061 mg L^-1 in the ROLC after treatment. The treatment cost was 3.86 USD kg_COD^-1, which was approximately 34% lower than that of previously reported electrochemical processes for ROLC treatment. These findings obtained with a real RO concentrate provide a foundation for scaling up this new electrochemical treatment approach.

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.

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.

One-step synthesis of novel Cu2ZnNiO3 complex oxide nanowires with tuned band gap for photoelectrochemical water splitting

Although alloying and nanostructuring offer a great opportunity for enhancing photoelectrochemical behavior and band gap tuning, these methods have not been investigated extensively. This article reports the synthesis of Cu2ZnNiO3 complex oxide nanowires (∼200 nm) grown on German silver alloy via a one-step optimized hydrothermal route and their utilization to split water photoelectrochemically. Surface characterizations were used to elucidate the formation mechanism of the Cu2ZnNiO3 complex oxide nanowires. The nanowires exhibited an exceptional visible light absorption extending from 400 to 1400 nm wavelengths with a tuned band gap of ∼2.88 eV calculated from the corresponding Tauc plot. In tests to split water photoelectrochemically, the nanowires generated a significant photocurrent of up to −2.5 mA cm−2 at −0.8 V versus Ag/AgCl and exhibited an exceptional photostability which exceeded 2 h under light-off conditions with no photocurrent decay. Band edge positions related to water redox potentials were estimated via Mott–Schottky and diffuse reflectance spectroscopy analysis with the density of charge carriers reaching as high as 5.15 × 1018 cm−3. Moreover, the nanowires generated ∼1100 µmol of H2 in 5 h. These photoelectrochemical results are much higher than the reported values for similar structures of copper oxide, zinc oxide and nickel oxide separately under the same conditions, which can be attributed to the advantages of Cu, Zn and Ni oxides (such as visible light absorption, photostability, and efficient charge carrier generation and transport) being combined in one single material. These promising results make German silver a robust material toward photoelectrochemical water splitting.

Enhanced decontamination of levofloxacin as toxic pharmaceutical residuals from water using CaO/MgO nanorods as a promising adsorbent

Novel MgO/CaO nanocomposite (MgO/CaO NRs) was synthesized by the hydrothermal method using diatomite porous frustules as a substrate under the microwave irradiation. The composite appeared as well crystalline rod-like nanoparticles with 52.3 nm as average particle size and 112.8 m²/g as BET surface area. The synthetic MgO/CaO NRs were addressed as a novel adsorbent for promising removal of levofloxacin (LVX) as pharmaceutical residuals. The adsorption studies revealed effective uptake of levofloxacin by MgO/CaO NRs with theoretical q_max of 106.7 mg/g and the equilibrium time of 720 min considering the best pH value (pH 7). The equilibrium studies highly fitted with the Langmuir model of monolayer adsorption considering the values of Chi-squared (χ²) and determination coefficient. The estimated adsorption energy from Dubinin–Radushkevich (0.2 kJ/mol) signifies physisorption mechanisms that might be coulombic attractive forces considering the kinetic studies. The thermodynamic addressing for the reactions verified their spontaneous and exothermic nature within a temperature range from 303 to 333 K. Additionally, the prepared MgO/CaO NRs show significant recyclability properties to be used in realistic remediation process and its uptake capacity is higher than several studied adsorbents in literature.

Graphitic mesoporous carbon-silica composites from low-value sugarcane by-products for the removal of toxic dyes from wastewaters

Highly porous carbon-silica composites (CSC) were prepared for the first time through a simple wet impregnation process and subsequent pyrolysis of low-value sugarcane by-products, namely molasses. These CSC materials demonstrate a distinct range of functionalities, which significantly differ from similar materials published in the literature. Importantly, the carbon-silica composites prepared at 800°C exhibited exceptional adsorption capacities for the azo-dye congo red (445 mg g-1), due to the graphitic carbon coating and unique functionality including C-O-C within the porous structure. Congo red adsorption capacity of the highly mesoporous graphitic carbon-silica composites significantly exceeds that of commercial activated carbon and silica, these carbon-silica composites therefore represent an effective step towards the development of porous bio-derived adsorbent for remediation of dye wastewaters. Both the porous properties (surface area and pore size distribution) and the functionality of the carbon coating were dependent on the temperature of preparation. The sustainable synthetic methods employed led to a versatile material that inherited the mesoporosity characteristics from the parent silica, demonstrating mesoporous volumes greater than 90% (as calculated from the total pore volume). Adsorption on the 800°C prepared carbon-silica composites demonstrated an excellent fit with the Langmuir isotherm and the pseudo-first-order kinetic model.

Excellent Oxygen Evolution Reaction of Activated Carbon-Anchored NiO Nanotablets Prepared by Green Routes

A sustainable and efficient electrocatalyst for the oxygen evolution reaction (OER) is vital to realize green and clean hydrogen production technology. Herein, we synthesized the nanocomposites of activated carbon-anchored nickel oxide (AC-NiO) via fully green routes, and characterized their excellent OER performances. The AC-NiO nanocomposites were prepared by the facile sonication method using sonochemically prepared NiO nanoparticles and biomass-derived AC nanosponges. The nanocomposites exhibited an aggregated structure of the AC-NiO nanotablets with an average size of 40 nm. When using the nanotablets as an OER catalyst in 1 M KOH, the sample displayed superb electrocatalytic performances, i.e., a substantially low value of overpotential (320 mV at 10 mA/cm2), a significantly small Tafel slope (49 mV/dec), and a good OER stability (4% decrease of overpotential after 10 h). These outstanding OER characteristics are considered as attributing to the synergetic effects from both the ample surface area of the electrochemically active NiO nanoparticles and the high electrical conductivity of the AC nanosponges. The results pronounce that the fully ecofriendly synthesized AC-NiO nanotablets can play a splendid role as high-performance electrocatalysts for future green energy technology.

Effective decontamination of As(V), Hg(II), and U(VI) toxic ions from water using novel muscovite/zeolite aluminosilicate composite: adsorption behavior and mechanism

Muscovite/phillipsitic zeolite was introduced as a novel inorganic composite of stunning adsorption properties. The composite was investigated in the uptake reactions of Hg(II), As(V), and U(VI) as highly toxic water contaminants considering different adsorption factors. The adsorption properties of muscovite/phillipsitic zeolite are highly dependent on the pH values and the best decontamination percentages can be obtained at pH 4, pH 5, and pH 5 for Hg(II), As(V), and U(VI), respectively. The kinetic studies demonstrated adsorption equilibrium for Hg(II), As(V), and U(VI) after 360 min, 300 min, and 360 min, respectively. The equilibrium modeling suggested monolayer uptake for all the metals and represented mainly by the Langmuir model considering both the values of determination coefficient and chi-squared (χ²). The estimated maximum capacities are 117 mg/g (Hg(II)), 122.5 mg/g (As(V)), and 138.5 mg/g (U(VI)) which are higher values than several studied adsorbents. The Dubinin-Radushkevich adsorption energies of Hg(II) (19.4 kJ/mol), As(V) (25.6 kJ/mol), and U(VI) (26.47 kJ/mol) signify chemical adsorption mechanisms and close to the obtained values for the ion-exchange process. Additionally, the composite is of high reusability properties and was applied effectively for five decontamination cycles. Graphical abstract.

Insight into the Adsorption and Photocatalytic Behaviors of an Organo-bentonite/Co3O4 Green Nanocomposite for Malachite Green Synthetic Dye and Cr(VI) Metal Ions: Application and Mechanisms

A green composite of organically modified bentonite supported by Co3O4 nanoparticles (OB/Co) was successfully fabricated and investigated as a potential eco-friendly, low-cost adsorbent and photocatalyst for promising removal of both malachite green dye (MG.D) and Cr(VI) ions. The composite showed high adsorption properties and achieved experimental q max values of 223 and 139 mg/g for MG.D and Cr(VI) after equilibration times of 360 min and 480 min for the inspected contaminants, respectively. The kinetic and equilibrium inspection reflected the best description of their adsorption behaviors by the pseudo-first-order kinetic model and the Langmuir isotherm model, respectively. This revealed favorable and homogeneous uptake of both MG.D and Cr(VI) in a monolayer form with theoretical Langmuir q max values of 343.6 and 194.5 mg/g, respectively. The theoretical adsorption energies of MG.D (0.6 kJ/mol) and Cr(VI) (0.5 kJ/mol) from the Dubinin-Radushkevich (D-R) model revealed physisorption properties that might be resulted from some types of Coulombic attractive forces, achieving theoretical q max values of 226.5 and 144.6 mg/g, respectively. The suggested adsorption mechanism was confirmed by the main mathematical parameters of thermodynamic studies that revealed physical, spontaneous, and exothermic uptake processes. Also, the composite showed high photocatalytic performance under visible light, which resulted in a 100% removal percentage of 100 mg/L of MG.D and Cr(VI) after about 180 and 240 min, respectively, from the adsorption equilibrium time.

Insight into the photocatalytic properties of diatomite@Ni/NiO composite for effective photo-degradation of malachite green dye and photo-reduction of Cr (VI) under visible light

Diatomite frustules decorated by nano Ni/NiO nanoparticles (Diatomite@Ni/NiO) were synthesized as a novel photocatalyst for effective degradation of malachite green cationic dye (M.G) and photocatalytic-reduction of Cr (VI) ions. The composite was characterized by different analytical techniques and revealed enhancing in the surface area (400 m²/g), 5.8 nm as average pore diameter and showed lower band gap energy (1.71 eV) than NiO as single phase. The photocatalytic activity of the composite in the removal of M.G and reduction of Cr (VI) was evaluated under visible light considering the pH, illumination time, catalyst mass, and the pollutants concentrations. The results revealed complete removal of 25 mg/L M.G can be achieved using 20 mg, 30 mg, 40 mg and 50 mg of the after 150 min, 90 min, 60 min, and 30 min, respectively. The complete degradation of 50 mg/L can be obtained after 240 min, 90 min, and 60 min using 20 mg, 40 mg, and 50 mg of the catalyst, respectively. This also was reported for the photocatlytic-reduction of 25 mg/L of Cr(VI) ions as the complete reduction was estimated after 180 min, 60 min and 30 min using 20 mg, 40 mg, and 50 mg, respectively. Also, 50 mg/L of Cr (VI) can be completely reduced after 240 min, 90 min, and 60 min using 20 mg, 40 mg, and 50 mg as catalyst dosage, respectively. The photocatalytic degradation of M.G controlled mainly by the generated electron-hole pairs and the superoxide species while the photocatalytic-reduction of Cr (VI) controlled mainly by the directly excited electrons of Ni/NiO and partially by the formed superoxide radicals. Hence, the synthetic diatomite@Ni/NiO composite can be considered as potential photocatalyst in the degradation of M.G dye and photoreduction of Cr (VI) ions.

Graphene/waste-newspaper cellulose composite aerogels with selective adsorption of organic dyes: preparation, characterization, and adsorption mechanism

Waste-newspaper cellulose/graphene composite aerogels were facilely synthesized via the sol–gel and freeze-drying processes for dye wastewater treatment.

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).

Evaluation of a novel dextran-based flocculant on treatment of dye wastewater: Effect of kaolin particles

Graft modified flocculants have recently received increasing attention in the field of water treatment as they have the combinative advantages of synthetic and natural polymeric flocculants. In this work, surface-active monomer benzyl(methacryloyloxyethyl)dimethylammonium chloride (BMDAC) was selected to graft on dextran (DX) with high molecular weight (10.3 × 10⁶ g/mol) produced through enzyme-catalyzed process in order to remove dissolved dyes from wastewater. The flocculant (DAB) was fabricated by ultrasound initiated polymerization technique, and the structure characterization of FTIR, ¹H/¹²C NMR, XRD and XPS spectrum confirmed the successful grafting. Then the Congo red (CR) removal efficiency by DAB was optimized based on the flocculation conditions, including wastewater initial pH, flocculant dosage and initial dye concentration. The effect of suspended solids on the removal of dyes was evaluated in kaolin-CR simulated wastewater. The results indicated that the optimal removal efficiency of CR was 68.1% and 88.2% in single CR and kaolin-CR flocculation system, respectively. The improvement of removal efficiency was attributed to the fact that partial CR molecules were adsorbed onto kaolin particles before flocculation, and were synergistically flocculated accompanied by kaolin particles. Finally, the flocculation mechanism was discussed by a detailed investigation of the zeta potentials, FTIR and XPS spectra of flocs, which can provide important reference for optimizing the flocculation conditions and designing novel high-performance flocculants.

The mineralization of oxalic acid and bio-treated coking wastewater by catalytic ozonation using nickel oxide

Coking wastewater after biological treatment still possesses potential environmental risk and should be mineralized further. This work focused on the mineralization of bio-treated coking wastewater using catalytic ozonation by NiO. First, oxalic acid, the typical by-product of advanced oxidation process (AOPs), was used to test the catalytic performance of NiOs, prepared by modified hydrothermal methods upon addition of different surfactants. This demonstrated that NiO upon addition of hexadecyltrimethylammonium (CTAB) had the best catalytic activity, due to its high concentration surface hydroxyl density and strong stability. Moreover, the best NiO was applied for the catalytic ozonation of bio-treated coking wastewater. Under our experimental conditions, the total organic carbon (TOC) removal reached 100% after 420 min. In addition, the spectroscopic analysis suggested that compounds with conjugated structures could be significantly removed by both ozonation and catalytic ozonation. Some of these substances were transformed into by-products with aliphatic C-C and O=C-O groups such as organic acids that can inhibit further mineralization.

Eco-friendly synthesis of graphene–chitosan composite hydrogel as efficient adsorbent for Congo red

A simple approach was utilized to synthesize graphene/chitosan-based hydrogel using glutaraldehyde as crosslinking agent in room temperature. The composite aerogel was used for removal of cationic and anionic dyes from aqueous solution. It showed high adsorption capacity towards Congo red as an anionic dye. Adsorption experiments were performed based on various parameters, such as initial Congo red concentration, solution pH and contact time. The kinetics data were analyzed using four different models and the pseudo-second-order model best described the adsorption of Congo red aerogel. The Equilibrium adsorption isotherm data indicated that equilibrium data were fitted to the Langmuir isotherm. The maximum dye adsorption capacity calculated from the Langmuir isotherm equation was 384.62 mg g⁻¹. Moreover, the aerogel was stable and easily recovered, and adsorption capacity was about 100% of the initial saturation adsorption capacity after being used three times.

Graphene/chitosan-based hydrogel was synthesized using glutaraldehyde as crosslinking agent in room temperature and it used for removal of Congo red dye from aqueous solution.

Synthesis of a hierarchical structured NiO/NiS composite catalyst for reduction of 4-nitrophenol and organic dyes

The synthesis approach of the catalyst is simple and facile. The NiO/NiS catalyst is effective and universal towards reduction. NiS facilitates electron transfer for reduction reactions.