Fabrication of mixed phase calcium ferrite and zirconia nanocomposite for abatement of methyl orange dye from aqua matrix: Optimization of process parameters

Remediation of Methyl Red Dye from Aqueous Solutions by Using Biosorbents Developed from Floral Waste

The disposal of biological waste into water bodies is a major global concern as it leads to water pollution resulting in the loss of plenty of revenue in the cleaning of water bodies. Here, in the present research work, sacred flowers were collected, segregated, sun-dried, and powdered. The dried floral powders (marigold and rose) were characterized by field emission scanning electron microscopy (FESEM), electron diffraction spectroscopy (EDS), Fourier transforms infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). The microscopy revealed the irregular spherical shape of the sheet-like structure whose size varies in microns. The EDS revealed the elemental composition which was dominated by mainly carbon and oxygen. The XRD shows the presence of carbon (10-25ɵ) in the amorphous form and the absence of any crystalline phase in the biosorbents. The FT-IR showed peaks that conformed to the presence of functional groups like -OH and a carbonyl group. The dried powders were used as an economical and eco-friendly biosorbent for the removal of methyl red (MR) dye from the aqueous solutions by batch adsorption study. After 60 minutes of contact time, the marigold powder (MGP) and rose petal powder (RPP) showed decolorization of 61.16% and 56.08% for 2 ppm of MR dye. The kinetic revealed that the dye removal reaction does not follow the pseudo-first-order as well as the pseudo-second-order. The utilization of such waste-based biosorbents will minimize solid waste and also will provide an economical biosorbent for the removal of environmental pollutants.

Tuning cationic/anionic dyes sorption from aqueous solution onto green algal biomass for biohydrogen production

Global water security and energy demands associated with uncontrollable population growth and rapid industrial progress are one of the utmost serious needs dangerously confronting humanity. On account of waste as a wealth strategy; a multifunctional eco-friendly sorbent (MGAP) from green alga was prepared successfully for remediation of cationic/anionic organic dyes and biohydrogen production. The structural and morphological properties of sorbent were systematically scrutinized by a variety of spectral analyses. The loading capacity of MGAP towards rhodamine B (RhB) and methyl orange (MO) dyes was inclusivity inspected under variable experimental conditions. The adsorption kinetics of both dyes onto MGAP was in good agreement with pseudo-second-order theory, whereas adsorption isotherms could fit well with the Langmuir model, with satisfactory loading capacities of 144.92 and 196.04 mg g^-1 for RhB and MO molecules, respectively. Moreover, ultra-sonication treatment admirably decreased the sorption equilibrium time from 180.0 min to 30.0 min. Furthermore, spent sorbent was managed particularly for biohydrogen production with a measured yield of 112.89, 116.59, and 128.17 mL-H₂/gVS for MGAP, MGAP-MO, and MGAP-RhB, respectively. Overall, the produced MGAP can potentially be offered up as a promising dye scavenger for wastewater remediation and biohydrogen production, thereby fulfilling waste management and circular economy.

Altered zirconium dioxide based photocatalyst for enhancement of organic pollutants degradation: A review

Heterogeneous advanced oxidation processes are a promising approach for cost-efficient removal of pollutants using semiconductors. Zirconium dioxide (ZrO₂) is an auspicious material for photocatalytic activity owning to its suitable bandgap, stability, and low cost. However, ZrO₂ suffers from fast recombination rate, and poor light harvesting ability. Nonetheless, extra modification has also shown improvements and therefore is worth investigating. The endeavour of this paper initially discusses the fundamentals with respect to reactive species, classification, and synthesis methods for ZrO₂. Furthermore, with particular consideration to stability and reusability, several additional modification approaches for ZrO₂-based photocatalysts such as doping and noble metals loading. Furthermore, the formation of heterojunctions has also been shown to boost photocatalytic activity while inhibiting charge carrier recombination. Finally, photocatalyst separation via magnetic-based photocatalysts are elucidated. As a result, ZrO₂-based photocatalysts are regarded as a promising emerging technology that warrants further development and research.

Removal of p-Nitrophenol from simulated sewage using steel slag: Capability and mechanism

The steel slag was investigated for the removal of p-nitrophenol (4-NP) from simulated sewage by batch adsorption and fixed-bed column absorption experiments. The results showed that the maximum adsorption capacity was 109.66 mg/g at 298 K, pH of 7, initial concentration 100 mg/L, and dose 0.8 g/L. The adsorption process fitted the Langmuir isothermal adsorption model and followed pseudo-second-order kinetic models, the activation energy of adsorption (Ea) was 10.78 kJ/mol, which indicated that the adsorption was single-molecule layer physical adsorption. The regeneration efficiency was still maintained at 84.20% after five adsorption-desorption cycles. The column adsorption experiments showed that the adsorption capacity of the Thomas model reached 13.69 mg/g and the semi-penetrating time of the Yoon-Nelson model was 205 min at 298 K. Fe₃O₄ was identified as the main adsorption site by adsorption energy calculation, XRD and XPS analysis. The FT-IR, Zeta potential, and ionic strength analysis indicated that the adsorption mechanism was hydrogen bonding interaction and electrostatic interaction. This work proved that steel slag could be utilized as a potential adsorbent for phenol-containing wastewater treatment.

Mesoporous carbon structure impregnated with 2D engineered zirconium: A sustainable adsorbent for the removal of dyes from the aqueous solution

The key designing of new breeds of the adsorbents aimed to improve the physical, chemical and textural morphology along with surface functionalization, selectivity toward the contaminants, and regenerations efficiency. In this aspect, two adsorbents named wet oxidative and ultrasonicated zirconium impregnated composite, have been synthesized through two routes, i.e., wet oxidation and ultrasonication. In wet oxidation method, carbon-based materials are oxidized using an oxidant followed by impregnation, while in ultrasonication assisted route, the impregnation is carried out using acoustic phenomenon. The characterization study revealed that the wet oxidation process is more competent in impregnating zirconium and developing diverse porosity and functionalities. The maximum adsorption capacity of wet oxidative adsorbent was 812 mg/g for Reactive Blue 19 and 203.18 mg/g for Methylene Blue, that accentuated the efficiency of the adsorbent over raw activated carbon. The electrostatic interaction, hydrogen-bonding and ligand exchange phenomenon are the involved adsorption mechanism for dyes. The regeneration study finally asserts that the wet oxidative adsorbent shows an insignificant decrease in its capacity up to the 5^th-cycle (i.e., 87.67% removal at 5^th cycle) as compared to raw AC (46.71% removal at 5th cycle). Further, a continuous fixed-bed column study revealed a significant correlation between experimental breakthrough data and kinetic data. Thus, the developed adsorbent has a sedulous adsorption capacity to remove the most stubborn toxic dyes and can be used in industrial-scale applications.

Design and preparation of functional azo linked polymers for the adsorptive removal of bisphenol A from water: Performance and analysis of the mechanism

In order to effectively remove refractory bisphenol A (BPA) from water, a novel nitrogen doped organic porous functional azo linked polymer (ALP-p) was designed and prepared according to the physicochemical characteristics of propane linked to two phenol hydroxyl groups. This ALP-p was synthesized with 98.5% yield, from pararosaniline and phloroglucinol, via the diazo coupling reaction to produce multiple adsorption functional groups of benzene ring, hydroxyl group and azo group. This functional material showed high adsorption capacity of 357.8 mg/g for 50 mg/L BPA, at 20 °C. The adsorption kinetics and isotherms were described by the pseudo-second-order and Langmuir model, respectively. The major adsorption mechanisms were attributed to the high specific surface area (259.8 m²/g) and pore volume (0.56 cm³/g) related surface adsorption and pore diffusion through porous stereoscopic stacking cavity anchorage. The functional group from the three-dimensional skeleton structures of ALP-p for BPA anchoring endowed chemisorption via π-π interaction between benzene rings and hydrogen-bonding (O-H⋯O, C-H⋯N, C-H⋯O and C-H⋯C) with the hydrogen atom of benzene ring, -OH from BPA and -OH, NN from ALP-p, respectively. The coexisting organic pollutants and alkali environment posed a negative effect on adsorption, while salinity had no significant effect on the process. The adsorption capacity and recovery of ALP-p were >93.5% and 81.6% after five cycles of operation.

Adsorption Characteristics and Molecular Simulation of Malachite Green onto Modified Distillers’ Grains

Adsorbent material was prepared using distillers’ grains (DG), which is a waste product of distilleries. The DG was pre-treated with NaOH and esterification-modified with CS2, which is a commonly used anionic modifier. The structure and morphology of the adsorbent was characterized by FTIR, XRD, EDS, SEM, BET, and zeta potential. The related mechanism of adsorption of malachite green (MG) onto modified distiller’s grains (MDG) was studied by adsorption experiments and molecular simulation techniques. The experimental results showed that CS2 successfully modified the DG fiber, and simultaneously yielded the MDG with a uniform pore distribution. MDG had a considerable adsorption capacity of 367.39 mg/g and a maximum removal rate of 96.51%. After eight adsorption–desorption cycle experiments, the adsorption removal rate of MDG to MG dye remained at 82.6%. The adsorption process could be fitted well by a pseudo-second-order kinetic model (the correlation coefficient R2 > 0.998) and Freundlich isotherm adsorption equation (the correlation coefficient R2 > 0.972). Moreover, the adsorption of MG dye by MDG is a spontaneous, endothermic, and increased entropy process. The results of molecular simulation showed that the mechanism of MG molecules onto MDG was mainly chemical adsorption. The adsorption performance of MG onto MDG was better and more stable than DG. Molecular simulation also provided a theoretical guidance of MDG adsorption–desorption for the research on recycling of DG resources.

Chitosan-Terephthalic Acid-Magnetic Composite Beads for Effective Removal of the Acid Blue Dye from Aqueous Solutions: Kinetics, Isotherm, and Statistical Modeling

A terephthalic acid-modified chitosan-magnetic nanocomposite (Cs-Tp@Fe₃O₄) was synthesized and characterized. The synthesized Cs-Tp@Fe₃O₄ was used in a batch process for the adsorptive removal of the acid blue 25 (AB-25) dye in aqueous solutions. The kinetic data were subjected to the pseudo-first-order, pseudo-second-order, Elovich, and intra-particle diffusion models, while the equilibrium data were evaluated with the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models. The effects of the initial dye concentration, contact time, and adsorbent dosage, as well as their interactions, on the removal efficiency were investigated using the design of experiments based on a central composite design, and the resultant data were modeled with the response surface methodology (RSM), artificial neural network (ANN), adaptive neuro-fuzzy inference system (ANFIS), and multiple linear regression (MLR) approaches. The adsorption process followed pseudo-first-order with good agreement between the experimental Q _e(exp) and calculated Q _e(cal.) amounts of dye adsorbed, as well as the values of correlation coefficient, R ² (0.999) and percentage of sum square error, % SSE (0.640). All the investigated adsorption isotherms fitted all models well in the order of Dubinin-Radushkevich > Langmuir > Freundlich > Temkin with R ² > 0.9 with the monolayer maximum adsorption capacity of 440.24 mg/g obtained from the Langmuir isotherm. The RSM model predicted the maximum removal efficiency at an optimum initial dye concentration of 19.11 mg/L, a contact time of 95.3 min, and an adsorbent dosage of 0.18 g. Statistically, the models were fitted in the order of RSM > ANN > ANFIS > MLR. These results indicated that the prepared Cs-Tp@Fe₃O₄ is an efficient adsorbent for the AB-25 dye removal with excellent stability for water treatment applications.

Synthesis of sewage sludge-based carbon/TiO2 /ZnO nanocomposite adsorbent for the removal of Ni(II), Cu(II), and chemical oxygen demands from aqueous solutions and industrial wastewater

The removal of heavy metal ions and organic materials from wastewater due to their toxicity is necessary. In the present study, the titanium dioxide/zinc oxide (TiO₂ /ZnO) nanocomposite has been coated on the sewage sludge carbon (SSC) surface and its application was investigated for the adsorption of Ni(II), Cu(II), and chemical oxygen demands (COD) reduction from aqueous solutions and industrial wastewaters in Eshtehard, Iran. The effect of adsorption parameters in a single system such as TiO₂ /ZnO ratio, TiO₂ /ZnO concentration, pH, adsorbent dosage, contact time, ionic strength, temperature, and initial concentrations of Ni(II), Cu(II), and COD was investigated on the adsorption capacity of synthesized SSC/TiO₂ /ZnO adsorbent. The pseudo-second order and Redlich-Peterson isotherm models were best described the kinetic and equilibrium data of Ni(II), Cu(II), and COD sorption. The maximum monolayer sorption capacities of Ni(II), Cu(II), and COD were found to be 62.3, 75.1, and 1,120.3 mg/g, respectively. The central composite design was used to investigate the interaction effects of pH and initial concentrations of Ni(II), Cu(II), and COD on the simultaneous removal of Ni(II), Cu(II), and COD from aqueous solutions in a ternary system. The potential of synthesized SSC/TiO₂ /ZnO adsorbent was investigated for Ni(II), Cu(II), and COD adsorption from industrial wastewaters of Iran. PRACTITIONER POINTS: The novel sewage sludge carbon/TiO₂ /ZnO adsorbent was synthesized. Adsorption of Ni(II), Cu(II), and chemical oxygen demands (COD) from industrial wastewaters was investigated. Maximum Ni(II), Cu(II), and COD sorption capacities were 62.3, 75.1, and 1,120.3 mg/g. Simultaneous removal of Ni(II), Cu(II), and COD was investigated in a ternary system.