Primary biosorption mechanism of lead (II) and cadmium (II) cations from aqueous solution by pomelo (Citrus maxima) fruit peels

Adsorption mechanism of aqueous Cr(vi) by Vietnamese corncob biochar: a spectroscopic study

Cr(vi) is highly toxic and carcinogenic, posing significant threats to health and ecosystems. This study utilizes solid waste from corncobs to synthesize biochar (CCBC) for the removal of Cr(vi) from water. The most effective Cr(vi) removal was achieved at pH 2.0, with a maximum adsorption capacity (Q m, Langmuir, mg g-1) of 38.1, higher than that of activated carbon (25.69), composite (35.84), and magnetic biochar (25.94) derived from corncobs. Brunauer-Emmett-Teller (BET) results indicated that Cr(vi) was adsorbed on the internal surface instead of external surface. Scanning electron microscope (SEM-mapping) images combined with the pHPZC value (7.6) demonstrated that Cr(vi) interacts with the material surface via electrostatic mechanisms. Energy-dispersive X-ray (EDX) spectra combined with Fourier-transform infrared (FTIR) spectra demonstrate that two key adsorption mechanisms in this study are surface adsorption (Cr(vi)-biochar) followed by the reduction of Cr(vi) to Cr(iii), allowing ion exchange adsorption to occur. X-ray diffraction (XRD) patterns indicate no precipitation on the surface, and the material remains stable after four reuse cycles. These results suggest that CCBC can be used as an efficient, cost-effective, and environmentally friendly adsorbent for Cr(vi) removal from water. This is the first study to combine spectroscopic methods and theoretical models to gain deeper insights into the Cr(vi) adsorption mechanisms onto CCBC.

The high adsorption performance of banana (Musa ABB Cv. Kluai 'Namwa') beaded materials modified with zinc and magnesium oxides for cadmium removal

Wastewater contaminated with cadmium is a concern because of its toxicity, persistence, and bioaccumulation to the environment, ecosystem, and human health, so it is required to remove cadmium(II) ions before releasing them to receiving water. Banana powder beads (BPB), banana powder doped ZnO beads (BPZB), banana powder doped MgO beads (BPMB), and banana powder doped ZnO + MgO beads (BPZMB) were synthesized as the novel cadmium adsorbents, and their characterizations, cadmium adsorption performances, cadmium adsorption patterns and mechanisms, thermodynamic study, and reusability were investigated. BPMB had the highest specific surface area of 16.60 m2/g and the smallest pore size of 1.69 nm than other materials. BPB was an amorphous structure, whereas BPZB, BPMB, and BPZMB were crystalline structures presenting their specific metal oxide peaks of ZnO or MgO. They were coarse surfaces and had a spherical shape consisting of C, O, Ca, Cl, and Na. Their main functional groups were O-H, C-H, C=O, C-O, and N-H. The points of zero charge of BPB, BPZB, BPMB, and BPZMB were 5.37, 6.75, 9.87, and 9.43. The cadmium removal efficiencies of BPB, BPZB, BPMB, and BPZMB were 89.18%, 96.62%, 99.59%, and 97.85%, and their qm values were 90.09, 232.56, 454.55, and 303.03 mg/g, respectively. Thus, the metal oxide helped to improve material efficiency, especially MgO. The Freundlich and pseudo-second-order kinetic models were good fit models for describing their adsorption patterns and mechanisms. The increasing temperature affected to decrease their cadmium adsorptions. They could be reused in more than 3 cycles of more than 73% of cadmium adsorption. The electrostatic interaction played an important role in describing their cadmium adsorptions. Therefore, BPBM was a good cadmium adsorbent for application in industrial wastewater treatment since it had a higher performance of cadmium adsorption than other materials.

Antimicrobial Activity against Fusarium oxysporum f. sp. dianthi of TiO2/ZnO Thin Films under UV Irradiation: Experimental and Theoretical Study

We deposited bare TiO2 and TiO2/ZnO thin films to study their antimicrobial capacity against Fusarium oxysporum f. sp. dianthi. The deposit of TiO2 was performed by spin coating and the ZnO thin films were deposited onto the TiO2 surface by plasma-assisted reactive evaporation technique. The characterization of the compounds was carried out by scanning electron microscopy (SEM) and powder X-ray diffraction techniques. Furthermore, density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were performed to support the observed experimental results. Thus, the removal of methylene blue (MB) by adsorption and posterior photocatalytic degradation was studied. Adsorption kinetic results showed that TiO2/ZnO thin films were more efficient in MB removal than bare TiO2 thin films, and the pseudo-second-order model was suitable to describe the experimental results for TiO2/ZnO (q e = 12.9 mg/g; k 2 = 0.14 g/mg/min) and TiO2 thin films (q e = 12.0 mg/g; k 2 = 0.13 g/mg/min). Photocatalytic results under UV irradiation showed that TiO2 thin films reached 10.9% of MB photodegradation (k = 1.0 × 10-3 min-1), whereas TiO2/ZnO thin films reached 20.6% of MB photodegradation (k = 3.9 × 10-3 min-1). Both thin films reduced the photocatalytic efficiency by less than 3% after 4 photocatalytic tests. DFT study showed that the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gap decreases for the mixed nanoparticle system, showing its increased reactivity. Furthermore, the chemical hardness shows a lower value for the mixed system, whereas the electrophilicity index shows the biggest value, supporting the larger reactivity for the mixed nanoparticle system. Finally, the antimicrobial activity against F. oxysporum f. sp. dianthi showed that bare TiO2 reached a growth reduction of 68% while TiO2/ZnO reached a growth reduction of 90% after 250 min of UV irradiation.

Simultaneous removal of phosphorus, zinc, and lead from oligotrophic ecosystem by iron-driven denitrification: Performance and mechanisms

Based on the current situation of complex pollution caused in surface water by oligotrophic condition and heavy metal release from river and lake bottom sediments. This study aimed to achieve the simultaneous removal of nitrate, phosphorus, Zn2+ and Pb2+ through microbial approach. At nitrate concentration of 4.82 mg L-1, carbon to nitrogen ratio of 1.5, pH of 6.0, and Fe2+ concentration of 5.0 mg L-1, the nitrate removal efficiency of Zoogloea sp. FY-6 reached 95.17%. The addition of pollutants under these conditions resulted in 88.76% removal of total phosphorus at 18 h, and 85.46 and 78.59% removal of Zn2+ and Pb2+ respectively, and there was competition for adsorption between Zn2+ and Pb2+. Extracellular polymers and fluorescence excitation-emission substrates confirmed that Fe2+ reduced heavy metal toxicity through promoting bacterial production of secretions and promotes denitrification as a carbon source. Meanwhile, contaminant removal curves and Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy demonstrated the synchronous removal of Zn2+ and Pb2+ mainly through biological action and the formation of nanoscale iron oxides. Biological-iron precipitation also provided adsorption sites for phosphorus. This research provides the theoretical foundation for applying microorganisms to restore oligotrophic source water (rivers and lakes) containing complex pollutants.

Effective adsorption of Pb(II) ion from aqueous solution onto ZSM-5 zeolite synthesized from Vietnamese bentonite clay

ZSM-5 zeolite was successfully synthesized from bentonite clay sourced from Lam Dong Province, Vietnam, using the hydrothermal method at 170 °C for 18 h. The synthesized ZSM-5 (SiO2/Al2O3 ratio ~ 34) exhibited a single phase with high crystallinity (91.8%), and a clear and uniform shape. In a detailed examination of the synthesized material's Pb(II) adsorptive capacity, various factors were taken into account, including pH, interaction time, ionic strength, and the amount of adsorbent. Isotherms and kinetics were examined to elucidate the uptake behavior. Study results suggested that Pb(II) ion uptake by ZSM-5 was most appropriately described by the Sips isotherm and intraparticle diffusion kinetic models. The calculated maximum monolayer adsorption capacity according to the Langmuir isotherm model was 48.36 mg/g. Furthermore, the adsorption mechanisms of Pb(II) on ZSM-5 involving electrostatic interactions, ion exchange, and diffusion into pores were demonstrated using the analytical techniques before and after Pb(II) adsorption. These findings demonstrate that ZSM-5 synthesized from bentonite clay exhibits an excellent adsorption capacity for Pb(II), resulting in promising applications for treating drinking water or aqueous industrial waste containing Pb(II) ions.

The Prediction of Cu(II) Adsorption Capacity of Modified Pomelo Peels Using the PSO-ANN Model

It is very well known that traditional artificial neural networks (ANNs) are prone to falling into local extremes when optimizing model parameters. Herein, to enhance the prediction performance of Cu(II) adsorption capacity, a particle swarm optimized artificial neural network (PSO-ANN) model was developed. Prior to predicting the Cu(II) adsorption capacity of modified pomelo peels (MPP), experimental data collected by our research group were used to build a consistent database. Then, a PSO-ANN model was established to enhance the model performance by optimizing the ANN's weights and biases. Finally, the performances of the developed ANN and PSO-ANN models were deeply evaluated. The results of this investigation revealed that the proposed hybrid method did increase both the generalization ability and the accuracy of the predicted data of the Cu(II) adsorption capacity of MPPs when compared to the conventional ANN model. This PSO-ANN model thus offers an alternative methodology for optimizing the adsorption capacity prediction of heavy metals using agricultural waste biosorbents.

Assessment of Cu(II) Removal from Aqueous Solutions by Modified Pomelo Peels: Experiments and Modelling

In this study, low-cost pomelo peel wastes were used as a bio-sorbent to remove copper ions (e.g., Cu(II)) from aqueous solutions. Prior to testing its Cu(II) removal capability, the structural, physical and chemical characteristics of the sorbent were examined by scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectroscopy, and Brunauer-Emmett-Teller (BET) surface area analysis. The impacts of the initial pH, temperature, contact time and Cu(II) feed concentration on the Cu(II) biosorption using modified pomelo peels were then assessed. Thermodynamic parameters associated to the biosorption clearly demonstrate that this biosorption is thermodynamically feasible, endothermic, spontaneous and entropy driven. Furthermore, adsorption kinetic data were found to fit very well with the pseudo-second order kinetics equation, highlighting that this process is driven by a chemical adsorption. Finally, an artificial neural network with a 4:9:1 structure was then established for describing the Cu(II) adsorption using modified pomelo peels with R² values close to 0.9999 and to 0.9988 for the training and testing sets, respectively. The results present a big potential use of the as-prepared bio-sorbent for the removal of Cu(II), as well as an efficient green technology for ecological and environmental sustainability.

Heavy Metal Contamination in the Aquatic Ecosystem: Toxicity and Its Remediation Using Eco-Friendly Approaches

Urbanization and industrialization are responsible for environmental contamination in the air, water, and soil. These activities also generate large amounts of heavy metal ions in the environment, and these contaminants cause various types of health issues in humans and other animals. Hexavalent chromium, lead, and cadmium are toxic heavy metal ions that come into the environment through several industrial processes, such as tanning, electroplating, coal mining, agricultural activities, the steel industry, and chrome plating. Several physical and chemical methods are generally used for the heavy metal decontamination of wastewater. These methods have some disadvantages, including the generation of secondary toxic sludge and high operational costs. Hence, there is a need to develop a cost-effective and eco-friendly method for the removal of heavy metal ions from polluted areas. Biological methods are generally considered eco-friendly and cost-effective. This review focuses on heavy metal contamination, its toxicity, and eco-friendly approaches for the removal of heavy metals from contaminated sites.

The effective Ni(II) removal of red mud modified chitosan from aqueous solution

This study used red mud modified with chitosan (RM/CS) as a novel adsorbent to remove Ni(II) ions from an aqueous solution. The adsorbent was characterized by the techniques of the BET method, X-ray diffraction (XRD), and scanning electron microscopy (SEM) analysis. According to the findings, the surface area of RM/CS is nearly doubled compared to CS, from 68.6 to 105.7 m².g^-1. The Ni(II) batch adsorption of RM/CS was performed as a function of pH value, contact time, and volume of adsorbent. Three isotherm adsorption models (Langmuir, Freundlich, and Sips) and three kinetic models (the pseudo-first-order, the pseudo-second-order, and the intra-diffusion models) were fitted with the experimental data to calculate the maximum adsorption capacity and to estimate the uptake in nature. The Langmuir monolayer adsorption capacity for Nickel (II) is 31.66 mg.g^-1 at a pH of 6.0, with an adsorption time of 180 min and a temperature of 323 K. The Ni(II) adsorption on RM/CS is the exothermic process and is controlled by the intra-diffusion model.

Simultaneous removal of nitrate, tetracycline, and Pb(II) by iron oxidizing strain Zoogloea sp. FY6: Performance and mechanism

Based on the prevalence of combined antibiotics and heavy metals contamination in the aquatic environment, this study utilized a microbial approach to achieve simultaneous removal of nitrate (NO₃^--N), tetracycline (TTC), and Pb(II). Zoogloea sp. FY6 could achieve an optimal NO₃^--N removal efficiency of 91.5% under C/N ratio of 2.0, at a pH of 6.3, and Fe(II) concentration of 20.23 mg L^-1 based on response surface methodology. Additionally, strain FY6 was further found to achieve 89.9 and 81.7% removal of TTC and Pb(II) at 6 h under the optimal conditions. Finally, the results of Fluorescence excitation-emission matrix, X-ray diffraction, Fourier transform infrared spectrometer, and X-ray photoelectron spectroscopy further proved that the biologically formed nanoscale iron oxides and biological action jointly led to the removal of TTC and Pb(II). This study provided a theoretical basis for the application of microbially driven process to remove multi-pollutants in micro-polluted water bodies.

Valorization of fruit wastes for circular bioeconomy: Current advances, challenges, and opportunities

The demands for fruits and processed products have significantly increased following the surging human population growth and rising health awareness. However, an enormous amount of fruit waste is generated during their production life-cycle due to the inedible portion and perishable nature, which become a considerable burden to the environment. Embracing the concept of "circular economy", these fruit wastes represent sustainable and renewable resources and can be integrated into biorefinery platforms for valorization into a wide range of high-value products. To fully realize the potential of fruit waste in circular bioeconomy and provide insights on future commercial-scale applications, this review presented the recycling and utilization of fruit wastes in various applications, particularly focusing on pollutant bioremediation, renewable energy and biofuel production, biosynthesis of bioactive compounds and low-cost microbial growth media. Furthermore, the challenges of efficient valorization of fruit wastes were discussed and future prospects were proposed.

Biosorption: A Review of the Latest Advances

Biosorption is a variant of sorption techniques in which the sorbent is a material of biological origin. This technique is considered to be low cost and environmentally friendly, and it can be used to remove pollutants from aqueous solutions. The objective of this review is to report on the most significant recent works and most recent advances that have occurred in the last couple of years (2019–2020) in the field of biosorption. Biosorption of metals and organic compounds (dyes, antibiotics and other emerging contaminants) is considered in this review. In addition, the use and possibilities of different forms of biomass (live or dead, modified or immobilized) are also considered.