Enhanced removal efficiency of clinoptilolite nano-particles toward Co(II) from aqueous solution by modification with glutamic acid

Modified coconut shell biochars (MCSBCs): Fabrication and their adsorptions for Pb(II)

The modified coconut shell biochars (MCSBCs) were fabricated and their adsorptions for Pb(II) were evaluated, in which waste coconut shell was used as the raw material, both ZnCl2 and KMnO4 were applied as the inorganic modifiers. FT-IR spectra, TGA, SEM and BET techniques were utilized to characterize their properties. It was spotted that the thermal stability of UCSBC could arrive at 500 °C. The BET specific surface areas of both Zn- and Mn-modified MCSBCs (485.137, 476.734 m2/g) were highly decreased as compared with that of UCSBC (3528.78 m2/g). In contrast, the average pore diameters of both Zn- and Mn-modified MCSBCs (3.295, 3.803 nm) were smaller than that of UCSBC (3.814 nm). These findings reveal that the modification of CSBC didn't change its pore size. Their adsorptions for Pb(II) were performed and some controlling factors involving pH, contact time, starting concentration and temperature were explored. Moreover, the experiment data were fitted via linear and non-linear techniques. It was found that the Langmuir maximal adsorption amounts of un-modified coconut shell biochar (UCSBC), Zn-modified and Mn-modified MCSBCs for Pb(II) could reach 31.653, 86.547 and 93.666 mg/g, respectively. Two-parameter kinetic models exposed that Pb(II) adsorption on UCSBC, Zn-modified and Mn-modified MCSBCs obeyed both the Lagergren first-order (non-linear R2 = 0.990, 0.954, 0.953, respectively) and Avrami fractional-order (non-linear R2 = 0.989, 0.946, 0.945, respectively) kinetic models. Two-parameter and three-parameter isotherm models verified that Pb(II) adsorption on UCSBC, Zn-modified and Mn-modified MCSBCs followed the Langmuir (non-linear R2 = 0.992, 0.997, 0.993, respectively) as well as Sips (non-linear R2 = 0.992, 0.997, 0.992, respectively) isotherm models. The computation of thermodynamic parameters evidenced that the modification of UCSBC via KMnO4 and ZnCl2 can effectively rise its adsorption for Pb(II), exhibiting promising applications in the handling of metal-bearing water.

Role of transition metals in coinage metal nanoclusters for the remediation of toxic dyes in aqueous systems

A difficult issue in chemistry and materials science is to create metal compounds with well-defined components. Metal nanoclusters, particularly those of coinage groups (Cu, Ag, and Au), have received considerable research interest in recent years owing to the availability of atomic-level precision via joint experimental and theoretical methods, thus revealing the mechanisms in diverse nano-catalysts and functional materials. The textile sector significantly contributes to wastewater containing pollutants such as dyes and chemical substances. Textile and fabric manufacturing account for about 7 × 105 tons of wastewater annually. Approximately one thousand tons of dyes used in textile processing and finishing has been recorded as being discharged into natural streams and water bodies. Owing to the widespread environmental concerns, research has been conducted to develop absorbents that are capable of removing contaminants and heavy metals from water bodies using low-cost technology. Considering this idea, we reviewed coinage metal nanoclusters for azo and cationic dye degradation. Fluorometric and colorimetric techniques are used for dye degradation using coinage metal nanoclusters. Few reports are available on dye degradation using silver nanoclusters; and some of them are discussed in detailed herein to demonstrate the synergistic effect of gold and silver in dye degradation. Mostly, the Rhodamine B dye is degraded using coinage metals. Silver nanoclusters take less time for degradation than gold and copper nanoclusters. Mostly, H2O2 is used for degradation in gold nanoclusters. Still, all coinage metal nanoclusters have been used for the degradation due to suitable HOMO-LUMO gap, and the adsorption of a dye onto the surface of the catalyst results in the exchange of electrons and holes, which leads to the oxidation and reduction of the adsorbed dye molecule. Compared to other coinage metal nanoclusters, Ag/g-C3N4 nanoclusters displayed an excellent degradation rate constant with the dye Rhodamine B (0.0332 min-1). The behavior of doping transition metals in coinage metal nanoclusters is also reviewed herein. In addition, we discuss the mechanistic grounds for degradation, the fate of metal nanoclusters, anti-bacterial activity of nanoclusters, toxicity of dyes, and sensing of dyes.

Efficient multi-ion adsorption using chitosan-malonic acid film: Enhancement using response surface methodology

The objective of this research is to conduct a comprehensive characterization of chitosan while also improving its attributes by crosslinking with malonic acid, with a focus on its efficacy in removing hexavalent chromium, arsenite and fluoride ions. Crosslinking chitosan in 1:0.5 mass ratio forming a film led to substantial enhancement in confiscation of these target pollutants. The characterization of the adsorbent involved several techniques, including FT-IR, TGA-DSC, SEM-EDX, XRD, and BET surface area analysis. In batch adsorption experiments, Chitosan-malonic acid (CMA) was employed to remove CrVI, AsIII and F- from aqueous solutions. These experiments were conducted while varying conditions such as pH, dosage, concentration, temperature, and time. Through the implementation of response surface methodology (RSM), parameters were optimized, resulting in over 95% removal of CrVI, AsIII and F- ions. The isotherm and kinetics data demonstrated a good fit with the Langmuir isotherm model and pseudo second-order kinetics, respectively. According to the Langmuir isotherm, the maximum adsorption capacities on CMA for CrVI, AsIII and F- were determined to be 687.05 mg g-1, 26.72 mg g-1 and 51.38 mg g-1 respectively under optimum pH of 4.0, 7.0 and 5.0 respectively under ambient temperature of 303 K. Thermodynamic analysis indicated that the adsorption process was spontaneous and driven by enthalpy. The regenerability of the adsorbent was validated through five adsorption-desorption cycles, signifying its reusability. An assessment of the adsorbent's sustainability indicated an eco-friendly synthesis, as reflected by the low E-factor value of 0.0028.

Synthesis and characterization of cylindrical electrode with sucrose binder as advanced electrode materials for copper 3D-electro-oxidation

This study produced a biomass-based cylindrical electrode containing sucrose (an organic binder). The Cu2+ removal performance of the synthesized sucrose-bonded cylindrical electrode was evaluated in a 3-phase 3-dimensional electro-oxidation reactor (3D-EO) and the classical electro-oxidation method (2D-EO). Sodium Dodecyl Sulfate (SDs) was grafted onto activated carbon and used as microelectrode in 3D-EO reactors. SDs grafting resulted in a 57% reduction in the micropores of activated carbon. Therefore, the surface area of carbon after grafting decreased from 1328 m2/g to 580 m2/g. The sucrose-bonded cylindrical electrode has a rich carbon structure and consists of 84.04 wt% C, 12.10 wt% O and 3.20 wt%Si. According to CV measurement, the sucrose-bonded cylindrical electrode gives a surface reaction against Cu2+ at voltages lower than -0.62 V. Increasing the potential difference from 1V to 3V in 2D-EO and 3D-EO processes led to the removal of Cu2+ from the solution. The 3D-EO reactor achieved a removal rate of 87.12% at 3V. The 100 ppm solution was treated with a 3D-EO reactor containing 6 g/L of PC/SDs400Ws for 60 min, successfully removing 91.22% of Cu2+.

Plasma-assisted in-situ preparation of L-cystine functionalized silver nanoparticle: An intelligent multicolor nano-sensing of cadmium and paracetamol from environmental sample

L-cystine (L-cys) functionalized plasmonic silver nanomaterial (Ag NPs) was fabricated toward the selective and sensitive detection of paracetamol and cadmium. The prepared L-cys-Ag nanoparticles (NPs) were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD) and fourier transform infrared spectroscopy (FTIR) analyses. SEM imaging show that Ag NPs was decorated on the surface of L-cysteine 3D cubic nanosheet. L-cys-Ag NPs showed selective and sensitive detection towards paracetamol and cadmium. The interference study confirms that the presence of other metal ions didn't inhibit the detection of cadmium by L-cys-Ag NPs. The limit of detection of paracetamol and cadmium by L-cys-Ag NPs was calculated to be 1.2 and 2.82 nM respectively. In addition, the real sample detection of paracetamol on blood serum and urine, and cadmium on STP were performed and the recovery percentage was above 97%. Further, the real sample analysis was performed in tap and drinking water and the recovery percentage was more than 98%. The analytic logic gate on the multicolour detection of cadmium and paracetamol was performed for the semi-quantitative monitoring of paracetamol and cadmium by L-cys-Ag NPs. The developed L-cys-Ag NPs were found to be an effective tool for the monitoring of cadmium in environmental water bodies and paracetamol in blood and urine.

Porous Carbons Derived from Desiliconized Rice Husk Char and Their Applications as an Adsorbent in Multivalent Ions Recycling for Spent Battery

Recycling of spent lithium-ion batteries (LIBs) has attracted increasing attentions recently on account of continuous growth demand for corresponding critical metals/materials and environmental requirement of solid waste disposal. In this work, rice husk as one of the most abundant renewable fuel materials in the world was used to prepare rice husk char (RC) and applied to recycle multivalent ions in waste water from hydrometallurgical technology dispose of spent LIBs. Rice husk char with specific surface area and abundant pores was obtained via pickling and desilication process (DPRC). The structural characterization of the obtained rice husk char and its adsorption capacity for multivalent ions in recycled batteries were studied. XRD, TEM, SEM, Raman, and BET were used for the characterization of the raw and the modified samples. The results show rice husk chars after desilication has more flourishing pore structure and larger pore size about 50–60 nm. Meanwhile, after desilication, the particle size of rice husk char decreased to 31.392 μm, and the specific surface area is about 402.10 m2/g. Its nitrogen adsorption desorption curve (BET) conforms to the type IV adsorption isotherm with H3 hysteresis ring, indicating that the prepared rice husk char is a mesoporous material. And the adsorption capacity of optimized DPRC for Ni, Co, and Mn ions is 7.00 mg/g, 4.84 mg/g, and 2.67 mg/g, respectively. It also demonstrated a good fit in the Freundlich model for DPRC-600°C, and a possible adsorption mechanism is proposed. The study indicates biochar materials have great potential as an adsorbent to recover multivalent ions from spent batteries.

Improvement in adsorption of Hg2+ from aqueous media using sodium-type fine zeolite grains

To increase the adsorption capability of Hg²⁺ from aqueous media, we prepared sodium-type fine zeolite grains with various particle sizes (denoted as ZE1, ZE2 and ZE3). The particle sizes of ZE1, ZE2 and ZE3 were 16.363 ± 0.365, 1.454 ± 0.357 and 0.607 ± 0.377 μm, respectively. Moreover, the CEC, specific surface area and pore volume were in the order ZE1 (42 mmol/g and 23.5 m²/g) < ZE2 (72 mmol/g and 67.1 m²/g) < ZE3 (135 mmol/g and 176.6 m²/g). Subsequently, the Hg²⁺ adsorption capability was investigated. The performance of tested agents on Hg²⁺ adsorbed was in the order ZE1 (5.0 mg/g) < ZE2 (9.4 mg/g) < ZE3 (20.2 mg/g). It was concluded that fine crystalline zeolite was important in enhancing the adsorption capability of Hg²⁺. In addition, the mechanism of adsorption of Hg²⁺ on the ZE samples was evaluated. Our results suggested that Hg²⁺ was exchanged with sodium ions in the interlayers of ZE samples with correlation coefficients of 0.966-0.979. Our findings revealed that these ZE samples constitute potential agents for the adsorption of Hg²⁺ from aqueous media.

Applications of Nano-Zeolite in Wastewater Treatment: An Overview

Nano-zeolite is an innovative class of materials that received recognition for its potential use in water and tertiary wastewater treatment. These applications include ion-exchange/sorption, photo-degradation, and membrane separation. The aim of this work is to summarize and analyze the current knowledge about the utilization of nano-zeolite in these applications, identify the gaps in this field, and highlight the challenges that face the wide scale applications of these materials. Within this context, an introduction to water quality, water and wastewater treatment, utilization of zeolite in contaminant removal from water was addressed and linked to its structure and the advances in zeolite preparation techniques were overviewed. To have insights into the trends of the scientific interest in this field, an in-depth analysis of the variation in annual research distribution over the last decade was performed for each application. This analysis covered the research that addressed the potential use of both zeolites and nano-zeolites. For each application, the characterization, experimental testing schemes, and theoretical analysis methodologies were overviewed. The results of the most advanced research were collected, summarized, and analyzed to allow an easy visualization and comparison of these research results. Finally, the gaps and challenges that face these applications are concluded.

Lanthanum ions decorated 2-dimensional g-C3N4 for ciprofloxacin photodegradation

The low band gap energy and high surface area two-dimensional materials allow it to tune its basic properties using surface decoration. Here, La³⁺ are decorated on two-dimensional graphitic carbon nitride using a simple and easily scalable chemisorption process with an adsorption capacity of 657.32 mg g^-1. In the X-ray diffraction (XRD) study, the positive slope of the W-H plot elucidates the tensile strain generation (0.103) in La³⁺ ions decorated 2D-g-C₃N₄ (La³⁺-2D-g-C₃N₄). The high-resolution transmission electron microscope (HR-TEM) study and the higher I_D/I_G ratio (0.82) in the Raman spectroscopy study confirm the more defects intensification in La³⁺-2D-g-C₃N₄. The reduction in band gap energy for La³⁺-2D-g-C₃N₄ (from 2.83 eV to 2.21 eV) has shown a good correspondence with the band structures study as obtained from the DFT study. In the DFT study, the significant contributions of N atoms in charge transfer validate the N 1s findings from the X-ray photoelectron spectroscopy (XPS) study for La³⁺-2D-g-C₃N₄. La³⁺-2D-g-C₃N₄ shows the photodegradation efficiency (93%) of ciprofloxacin under UV irradiation, which is superior to pristine 2D-g-C₃N₄ (82%) as well as other g-C₃N₄ based nanocatalysts. Also, La³⁺ decoration results in enhancement (32.3%) in photodegradation kinetics rate. The degradation and kinetics studies in the presence of different scavengers ensure that the O₂- and OH^- radicals are mostly responsible for the ciprofloxacin photodegradation. The Liquid chromatographic-mass spectroscopy and the high-performance liquid chromatography studies confirm the photodegradation. The reusability of La³⁺-2D-g-C₃N₄ is tested up to the fifth cycle. FTIR and UV-visible absorption spectroscopy confirm the stability of the used photocatalyst.

Utilization of rice husk and waste aluminum cans for the synthesis of some nanosized zeolite, zeolite/zeolite, and geopolymer/zeolite products for the efficient removal of Co(II), Cu(II), and Zn(II) ions from aqueous media

In this paper, rice husk and waste aluminum cans were exploited as silicon and aluminum sources, respectively for the low-cost synthesis of some nanosized zeolite, zeolite/zeolite, and geopolymer/zeolite products. XRD confirmed that the synthesized geopolymer/zeolite products are geopolymer/zeolite A (has a crystallite size of 58.44 nm & abbreviated as G1) and geopolymer/faujasite (has a crystallite size of 25.58 and 20.26 nm & abbreviated as G2 and G3, respectively). Also, the synthesized zeolite products are sodium aluminum silicate hydrate (has a crystallite size of 27.65 and 41.85 nm & abbreviated as H1 and H2, respectively). Besides, the synthesized zeolite/zeolite product is sodium aluminum silicate hydrate/zeolite A (has a crystallite size of 66.01 nm and abbreviated as H3). Moreover, the synthesized products were characterized using other tools such as HR-TEM, FE-SEM, EDX, and FT-IR. The synthesized products were efficiently applied for removing Co(II), Cu(II), and Zn(II) ions from aqueous media and wastewater which was taken from Abuzaabal- Qalyubiyah-Egypt. The maximum uptake capacity of G3 sample toward Co(II), Cu(II), and Zn(II) ions is 134.24 ± 1.26, 126.26 ± 0.32, and 131.93 ± 0.87 mg/g, respectively. The uptake of the studied metal ions is spontaneous, chemical, exothermic, and fitted well with the Langmuir isotherm and pseudo-2nd-order kinetic model.

Efficient recovery of Cu(II) by LTA-zeolites with hierarchical pores and their resource utilization in electrochemical denitrification: Environmentally friendly design and reutilization of waste in water

Water pollution seriously endangers human health and the environment. Here we prepared and tested mesoporous LTA zeolites for the adsorption of Cu(II) from aqueous media and the captured copper was further used for electrochemical nitrate reduction. The prepared hierarchically porous LTA exhibited a high capacity (341.5 mg g^-1) for Cu(II) adsorption, following the pseudo-second-order kinetic and Freundlich adsorption isotherm models well. The Cu-LTA sample was characterised by various analytical methods, and Cu(I) species were identified as the active sites for nitrate electrochemical reduction. Based on the spectral characterization and reducibility, strong metal-support interaction was found between copper and LTA, which is beneficial to the dispersion of active sites and their contacts with nitrates. In total, 10.1 g-N-NO₃ g^-1-Cu was reduced over the Cu-LTA-modified cathode in a three-electrode system with high N₂ selectivity (92.1 %). Compared to purely microporous zeolites, mesoporous LTA has a higher capacity for Cu(II) removal and nitrate reduction. The mesoporous structure allows easy access to the inner active sites with low diffusion resistance. The low Tafel slope and high current density confirm the high activity of the mesoporous Cu-LTA, making it a promising and efficient material for the removal and reuse of heavy metal ions.

Removal of Pb (II) from aqueous solution using nanoadsorbent of Oryza sativa husk: Isotherm, kinetic and thermodynamic studies

This research focus on the removal of Pb (II) ions from aqueous solution by adsorption process using nanoadsorbent developed from agricultural waste Oryza sativa husk (OSH). Surface morphology of nanoadsorbent was analyzed by FE-SEM, elemental composition by EDX and size by AFM. Attachment of functional groups on nanoadsorbent was determined by FTIR. The effect of pH, dose, contact time, initial concentration and temperature were investigated. Optimum adsorption of lead at pH 8, contact time 70 min at 60 °C temperature with 0.6 g/50 mL nanoadsorbent dose obeyed pseudo second order kinetic model with R² 0.996. Pb (II) adsorption was analyzed by Freundlich, Langmuir and Temkin models. Freundlich isotherm model with correlation coefficient R² 0.999 was best fitted. Thermodynamic parameters anticipated the adsorption process to be endothermic and spontaneous. Post adsorption elution was carried out successfully. Results demonstrate that OSH is a low cost and eco-friendly choice for Pb (II) remediation.

Determination of acidity in metal incorporated zeolites by infrared spectrometry using artificial neural network as chemometric approach

The NH₃-TPD analysis is a costly and tedious method to determine zeolites acidity. Thus, to do so, FTIR spectroscopy was quantitatively used as a fast and cost-effectively method. Back-propagation artificial neural network (BP-ANN) was used for the analysis of multivariate base on the characteristic absorbance of 11 zeolite samples after metal substitution in the ~3612 cm^-1 region. The successive projection algorithm (SPA) was conducted for the uninformative variable elimination and feature selection strategies. The effect of pre-processing methods (e.g. MC and MSC) was examined. It is observed after using MSC for minimizing the light scattering effect and signal-to-noise correction, the minimum mean squared error (MSE) value of the testing set data reduced from 5.36 × 10^-2 to 2.19 × 10^-4 and R_tot increases from 0.91 to 0.99. Also, the results of nonparametric Wilcoxon t-test and Sign test methods also confirmed that there is no clear difference between the zeolite acidity obtained by two conventional method and the proposed method.

Efficient Selective Removal of Pb(II) by Using 6-Aminothiouracil-Modified Zr-Based Organic Frameworks: From Experiments to Mechanisms

We report an efficient, reusable, and selective 6-aminothiouracil (ATA)-modified Zr(IV)-based adsorbent (defined as UiO-66-ATA(Zr)) for lead ion removal in water. The adsorption equilibrium time and the maximum sorption capacity of UiO-66-ATA(Zr) for Pb(II) are, respectively, 120 min and 386.98 mg/g at pH 4 and 298 K. The Pb(II) removal rate reaches 96% at 60 min and exceeds 99% at the equilibrium state in the pH range of 2.0-5.8. Hill and pseudo-second-order models can well describe the sorption process. Pb(II) adsorbing onto UiO-66-ATA(Zr) is an irreversible, favorable chemisorption process with multimolecule participation and film diffusion control. The calculations of density functional theory, the experimental results, and the characterization analyses suggest that the binding mechanisms are the chelation and ion-exchange/electrostatic interactions between hydroxyl/amino/sulfhydryl groups of UiO-66-ATA(Zr) and Pb(II). Besides, UiO-66-ATA(Zr) has a better affinity to Pb(II) than the coexisting ions in water and an excellent repeatability at eight cycles of adsorption. Moreover, the thermodynamic study shows that UiO-66-ATA(Zr) adsorbing Pb(II) is an endothermic reaction. Thus, UiO-66-ATA(Zr) is a prospective sorbent for Pb(II) removal under the initiative of environmental protection and water purification, and this work may also provide an idea for industrial catalysis.

Magnetically modified hydroxyapatite nanoparticles for the removal of uranium (VI): Preparation, characterization and adsorption optimization

Recently, magnetically modified nanomaterials have gained a great interest in the field of wastewater remediation. In this regard, the present work introduces a facile microwave-assisted pathway for the preparation of magnetically modified hydroxyapatite nanoparticles (MNHA) and evaluates its adsorption capability towards the removal of uranium (VI) ions from wastewaters. The prepared magnetic nanocomposite went through a full characterization procedure using different techniques, such as transmission electron microscope (TEM), X-ray diffraction (XRD), FT-IR, Brunauer-Emmett-Teller (BET) surface area measurements and magnetization curve. Involvement of the prepared MNHA in the remediation of wastewater containing U(VI) ions was investigated and the factors that influence the adsorption capacity were considered and optimized. The adsorption's optimum pH was found to be 5.0 and equilibrium was attended after 120 min. A maximum adsorption capacity of 310 mg/g was achieved after 120 min at 25 °C. The experimental data were well explained by Langmuir adsorption isotherm model. Kinetically, the adsorption process follows the pseudo-second order model. Thermodynamically, it is endothermic, irreversible and spontaneous adsorption process. Removal of U(VI) ions was found to take place via complex formation between the phosphate groups on the adsorbent and uranyl ions. The recovery of U(VI) ions from MNHA beads and the reusability of the spent beads were also explored. It was concluded that the prepared MNHA nanocomposite is simple, fast, ecofriendly adsorbent for the removal of U(VI) ions from water with excellent adsorption capacity.

Enhanced fluoride removal by hierarchically porous carbon foam monolith with high loading of UiO-66

Environmental concern associated with excess fluoride has intrigued the unceasing exploration of new multifunctional hybrid materials to mitigate any undesirable consequence to human health. Herein, a novel hybrid monolith has been successfully fabricated via a facile in-situ growth strategy for highly efficient defluoridation from contaminated waters, in which homogeneously dispersed UiO-66 particles are perfectly anchored on three dimensional (3D) porous carbon foam (CF). Benefiting from fully exposed active sites, excellent pore accessibility and efficient mass transport, the integrated UiO-66/CF hybrid monolith exhibits fast adsorption kinetics, and outstanding uptake capacity toward fluoride as high as 295 mg g^-1, which greatly outperforms the previously reported adsorbents. Furthermore, the fluoride removal efficiency of the spent monolith can reach up to 70% after four cycles, accompanied by facile separation nature and outstanding water stability. More significantly, the resulting UiO-66/CF packed column (0.36 g) can continuously treat 400 mL of F^- solution with 6.2 mg L^-1 before the breakthrough point occurs, highlight its potential feasibility for fluoride removal in the practical applicability.

Chemical reduction of methylene blue in the presence of nanocatalysts: a critical review

Methylene blue (MB) (3,7-bis (dimethylamino)-phenothiazin-5-ium chloride) is a harmful pollutant and has been long been known for its detrimental effects on human health. Over the recent years, many strategies including reduction, oxidation, biological and photochemical degradation have been reported for converting this harmful dye into commercially useful products. Among the aforementioned strategies, the nanocatalytic reduction of MB into its reduced counterpart, i.e. leucomethylene blue, is considered more preferable because it has been reported to have numerous applications in various industrial fields in the academic literature. The reduction of MB is the kinetically unfavorable reaction. Henceforth, various nanocatalytic systems utilizing different kinds of stabilization mediums have reportedly been used for speeding up this particular reaction. This article attempts to not only describe the fundamental properties of the reduction reaction of MB but also present the classification of the recently reported nanocatalytic assemblies on the basis of the utilized supporting medium. Various techniques used for the characterization of nanocatalytic systems reported for the reduction of MB have been summarized in this review. The thermodynamics, kinetics and mechanistic studies of this nanocatalytic reaction have also been narrated here. This critical review has been written comprehensively to abridge the recent research progress in the assemblage of nanocatalytic systems used for the reduction of MB and to propose some new ideas for further development in this area.

An Innovative Dual-Column System for Heavy Metallic Ion Sorption by Natural Zeolite

This study investigates the design and performance of a novel sorption system containing natural zeolite. The apparatus consists of packed, fixed-bed, dual-columns with custom automated controls and sampling chambers, connected in series and stock fed by a metering pump at a controlled adjustable distribution. The purpose of the system is to remove heavy metallic ions predominately found in acid mine drainage, including lead (Pb2+), copper (Cu2+), iron (Fe3+), nickel (Ni2+) and zinc (Zn2+), combined in equal equivalence to form an acidified total 10 meq/L aqueous solution. Reported trends on the zeolite’s preference to these heavy metallic ions is established in the system breakthrough curve, as Pb2+ >> Fe3+ > Cu2+ > Zn2+ >> Ni2+. Within a 3-h contact period, Pb2+ is completely removed from both columns. Insufficient Ni2+ removal is achieved by either column with the promptest breakthrough attained, as zeolite demonstrates the least affinity towards it; however, a 48.97% removal is observed in the cumulative collection at the completion of the analysis period. The empty bed contact times for the first and second columns are 20 and 30 min, respectively; indicating a higher bed capacity at breakthrough and a lower usage rate of the zeolite mineral in the second column. This sorption system experimentally demonstrates the potential for industrial wastewater treatment technology development.

Kinetic Modelling of the Removal of Multiple Heavy Metallic Ions from Mine Waste by Natural Zeolite Sorption

This study investigates the sorption of heavy metallic ions (HMIs), specifically lead (Pb2+), copper (Cu2+), iron (Fe3+), nickel (Ni2+) and zinc (Zn2+), by natural zeolite (clinoptilolite). These HMIs are combined in single-, dual-, triple-, and multi-component systems. The batch mode experiments consist of a total initial concentration of 10 meq/L normality for all systems, acidified to a pH of 2 by concentrated nitric (HNO3) acid. A zeolite dosage of 4 g per 100 mL of synthetic nitrate salt aqueous solution is applied, for a contact period of 5 to 180 min. Existing kinetic models on HMIs sorption are limited for multi-component system combinations. Therefore, this study conducts kinetic analysis by both reaction and diffusion models, to quantify the sorption process. The study concludes that the process correlates best with the pseudo-second-order (PSO) kinetic model. In the multi-component system combining all five HMIs, the initial sorption rate and theoretical equilibrium capacity are determined as 0.0033 meq/g·min and 0.1159 meq/g, respectively. This provides significant insight into the mechanisms associated with the sorption process, as well as contributing to the assessment of natural zeolite as a sorbent material in its application in industrial wastewater treatment.

Efficient Removal of Cobalt from Aqueous Solution by Zinc Oxide Nanoparticles: Kinetic and Thermodynamic Studies

This article deals with the removal of cobalt ions using zinc oxide nanopowder. The nanomaterial was prepared via the sol–gel method under supercritical drying. The nanomaterial was characterised via XRD, SEM, EDX, FTIR, and BET surface area techniques. The kinetics, equilibrium, and thermodynamic studies of the metal ions adsorption on the nanomaterial were conducted in batch mode experiments by varying some parameters such as pH, contact time, initial ion concentrations, nanoparticles dose, and temperature. The data revealed significant dependence of the adsorption process on concentration, and the temperature was found to enhance the adsorption rate indicating an endothermic nature of the adsorption. The adsorption complied well with the pseudo-second-order kinetics model. The adsorption process was found to match the Langmuir adsorption isotherm. The ZnO nanoparticles could successfully remove up to 125 mg·g−1 of Co(II) ions at elevated temperature. The metal ions adsorption could be described as an endothermic, spontaneous physisorption process. A mechanism for the metal ions adsorption was proposed.

Mechanism and performance for adsorption of 2-chlorophenol onto zeolite with surfactant by one-step process from aqueous phase

To decrease the power, material, and time consumption in wastewater treatment, a one-step process was performed to remove 2-chlorophenol (2-CP) from aqueous phase using zeolite and cetyltrimethylammonium bromide (CTAB). Compared with the traditional two-step process, the one-step process used in this study achieved almost eight times higher 2-CP adsorption capacity within a shorter time and maintained high removal efficiencies (around 65%) in reuse tests, thus becoming an efficient and economically acceptable alternative process. For the one-step process, the kinetic data fitted well with a nonlinear pseudo-second-order model, and the isotherm data fitted well with the Dubinin-Astakhov (DA) model. The uptake of 2-CP was highly dependent on pH, increasing in the pH range of 3-6. The enhanced 2-CP removal in a one-step adsorption process can be explained by the larger amount of surfactant loading (≥0.056mmol/g), as determined from the total organic carbon (TOC) and zeta potential. Due to the formation of a loose CTAB bilayer, the hydrophobic partition and the interaction with the positively charged "head" of CTAB bilayers were decisive for the enhancement of pollutant adsorption. Therefore, organic pollutants could be removed from water alongside the synthesis of hydrophobic zeolite in a one-step process, which is a promising technology for the in-situ treatment of organic wastewater.