Removal of doxorubicin hydrochloride and crystal violet from aqueous solutions using spray-dried niobium oxide coated with chitosan-activated carbon: Experimental and DFT calculations

Spray-dried niobium oxide coated with chitosan-activated carbon (NIC) was synthesized and used to remove doxorubicin hydrochloride and crystal violet from aqueous solutions under different parameters such as solution pH (2, 4, 6, and 8), contact time (1 to 9 h), initial concentration (20 to 200 mg L-1), and competing ions (0.1 M of CaCl2 and NaCl). The addition of 5 % chitosan-activated carbon to the matrix of niobium oxide slightly increased the specific surface area from 26 to 30 m2 g-1, with the introduction of a carboxylic functional group. This led to an increase in the amount of adsorbed doxorubicin hydrochloride (DOH) from 30 to 44 mg g-1 and that of crystal violet (CV) from 15 to 32 mg g-1 from the initial respective 100 mg L-1 at pH 8. The data from the concentration study fitted into Liu isotherm having adsorption capacity of 128 and 57 mg g-1 for DOH and CV respectively, while pseudo first and second order are more suitable for adsorption kinetics. The additional functional groups on the IR spectrum of NIC after the adsorption of DOH and CV confirmed the interaction between NIC and the adsorbates' molecules. The mechanism of adsorption was supported by DFT calculations.

Removal and environmentally safe disposal of As(III) and As(V)-loaded ferrihydrite/biosilica composites

Pure ferrihydrite and ferrihydrite-biosilica composite were synthesized and studied for the removal of As(III) and As(V). The synthesized materials have an adsorption capacity higher than some reported materials in the literature - 140 and 90 mg g^-1 for As(III) and As(V), respectively. The pH of the solution was shown to impact greatly on As(V) adsorption, but not on As (III), which is stable as a protonated, uncharged oxyanion, at pH < 9.2. The adsorption products were subjected to thermal treatment (500 °C for 2 h), promoting ferric arsenate formation. The adsorbed As on ferrihydrite (Fh) was shown to inhibit the phase transformation of Fh to hematite. More so, thermal treatment was shown to oxidize As(III) to As (V). The changes in the adsorption residues after thermal treatment also had an impact on As mobility. The As (III) associated with the Fh phase increased from 42 to 95%, according to a sequential extraction protocol. Therefore, this work presents a process for As removal, followed by thermal treatment of arsenic-loaded ferrihydrites which enables environmentally safe disposal of As residues.

Reducing the negative impact of ceftriaxone and doxycycline in aqueous solutions using ferrihydrite/plant-based composites: mechanism pathway

The adsorption of ceftriaxone (CET) and doxycycline (DOX) from aqueous solution using ferrihydrite/plant-based composites (silica rice husk) to reduce their negative impact on the ecosystem was adequately studied. On the other hand, phosphate and humic acid are often found in water and soil; in view of this, their effects on the adsorption of CET and DOX were investigated. The results showed that the removal of ceftriaxone decreased with an increase in pH, while that of doxycycline did not. Ferrihydrite with 10% silica rice husk (Fh-10%SRH) has the highest maximum adsorption capacity of 139 and 178 mg g^-1 for CET and DOX, respectively, at room temperature based on Liu's adsorption isotherm. This implies that the presence of silica rice husk increases CET and DOX uptake due to an increase in the pore volume of FH-10%SRH. The results showed that phosphate had a significant inhibition role on CET adsorption and minor on DOX, whereas humic acid salt affected neither case. Increase in temperature up to 333 K favored the adsorption of both contaminants. The proposed adsorption mechanisms of ceftriaxone are electrostatic interaction, n-π interaction, and hydrogen bond, while that of DOX entails n-π interaction and hydrogen bond.

Synergistic effect of a spinel ferrite on the adsorption capacity of nano bio-silica for the removal of methylene blue

The synergistic effect of CoFe₂O₄ on the capacity of bio-silica extracted from rice husk for the removal of methylene blue (MB) was investigated. The novel composite of cobalt ferrite/nano bio-silica was prepared by dispersing cobalt and iron salt in ratio 1:2 in a solution containing bio-silica, calcined at 700°C and characterized. The adsorption capacity of the composite (253.6 mg g^-1) was higher than that of bio-silica (52.6 mg g^-1), and the process was exothermic and spontaneous. Langmuir and Freundlich models were applicable to explain the adsorption isotherm, while pseudo-second-order and Elovich are best applicable for the kinetics mechanism. The amount of MB that was removed, increased with an increase in ionic strength due to dimerization of MB. Regeneration and reusability of the adsorbents showed that they are economically viable. Energy-filtered transmission electron microscopy (EFTEM) and Fourier transformed infrared (FTIR) analysis of MB-loaded adsorbent confirmed the adsorption of MB.

Comparative studies of chitosan and carboxymethyl chitosan doped with nickel and copper: Characterization and antibacterial potential

The study focused on the preparation and antibacterial evaluation of chitosan (CHT), carboxymethyl chitosan (CMC) and their respective metal composites. All the samples were characterized using Fourier Transform Infrared (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The antibacterial potentials of the samples were tested against Escherichia coli, Klebsiella sp., Pseudomonas aeruginosa A, and Pseudomonas aeruginosa B. SEM results revealed different changes in samples surfaces as a result of chemical modification. EDS revealed the presence of Ni and Cu in the composites. XRD spectra of CMC showed that the crystalline region of CHT was reduced by the modification. The antibacterial results indicated that the samples had inhibitory and bactericidal effects against Escherichia coli and Klebsiella sp. at 1000, 500, and 250 mg mL^-1. The study showed that CMC and CMC-metal composites performed better at inhibiting the growth of microorganisms than CHT and CHT-metal composites.

Effects of aluminum and soil mineralogy on arsenic bioaccessibility

A comprehensive characterization was performed to investigate the composition and mineralogy of soils from a gold mining region and their correlation with arsenic (As) total concentration and its bioaccessible fraction. The arsenic bioaccessible (BAC) fraction was determined through in vitro test and calculated as the ratio between the amounts of As released and the total As concentration in the soil sample. Among the minor constituents of environmental concern, only arsenic is significantly higher (median of 748.0 mg kg^-1) than the national guidelines (agricultural, 35 mg kg^-1 and residential, 55 mg kg^-1). All the other trace elements showed concentrations below the investigation values established for residential areas. The mean bioaccessible As was 7.0 mg kg^-1, with a median value of 4.4 mg kg^-1, and a median As BAC percentage of 0.7%. The Brunauer-Emmett-Teller (BET) surface area showed a consistent increase with the increase of the acid-soluble Al content in the soil samples. The distribution of As in the soil samples is not correlated with the abundance of As-minerals and the fraction of adsorbed As. Arsenic was shown to be trapped in oriented aggregates of crystalline (Al-)Fe-(hydr)oxides nanoparticles (the main metalloid reservoirs), as demonstrated by scanning and transmission electron microscopy analyses. This unique pattern supports the significant difference between total As concentration and the bioaccessible amount. There was a positive correlation between soluble Al (within the Fe-(hydr)oxides phases and minor gibbsite) and As concentration in the soil samples, and a negative correlation with bioaccessible As. Therefore, although Al in the soil is associated with high As levels, it also makes the metalloid less bioaccessible. The risk to human health from As exposure to these soils is low.

Adsorption of Methylene blue and Congo red from aqueous solution using synthesized alumina-zirconia composite

Alumina-zirconia (Al₂O₃-ZrO₂) composite was prepared by combustion method and used to remove Congo red and Methylene blue from aqueous solutions. It was characterized using SEM-EDS, XRD and gas adsorption techniques. The results obtained from gas adsorption and SEM agree with each other, showing meso- and macro-porosity of inter-agglomerate pores. The removal of the two dyes was pH dependent, acidic pH favoured Congo red removal, while basic pH favoured Methylene blue. The, mechanism of adsorption was not limited to electrostatic attraction between the adsorbent and the dye molecules. Adsorption kinetic of both dyes was consistent with Pseudo-second-order model. The data obtained fitted to Langmuir and Liu isotherm models, with the maximum adsorption capacity of 57. 50 and 53.44 mg g^-1 for Congo red and Methylene blue, respectively. The thermodynamic parameters indicated that the adsorption is spontaneous and exothermic. The mechanism of adsorption was elucidated using XRD and FTIR techniques.

Comparative adsorption mechanism of doxycycline and Congo red using synthesized kaolinite supported CoFe2O4 nanoparticles

Kaolinite supported CoFe₂O₄ (KCF) was synthesized and employed to adsorb doxycycline (DOX), an antibiotic and Congo red (CR), a dye from aqueous solution. The prepared KCF nanocomposite was treated in a muffle furnace at 300, 500 and 700 °C, and thereafter characterized. X-ray diffractogram revealed structural damage of kaolinite and appearance of distinct peaks of CoFe₂O₄ with an increase in calcination temperature, while transmission electron microscopy (TEM) images showed that CoFe₂O₄ nanoparticles were supported on the lamellar surface of kaolinites. Comparative adsorption mechanism of the two targeted contaminants showed that adsorption of DOX was influenced by hydrogen bond and n-π interaction, while that of CR was due to hydrophobic interaction and hydrogen bond. However, the adsorption of the two contaminants was best fitted to the isotherm that was proposed by Langmuir, with a monolayer maximum adsorption capacity of 400 mg g^-1 at 333 K for DOX, and 547 mg g^-1 at 298 K for CR. The removal of DOX from aqueous solution was favored by an increase in temperature (endothermic), while that of CR was exothermic. Thermodynamics studies confirmed that the adsorption of the two contaminants is feasible and spontaneous. The presence of natural organic matter (NOM) did not affect the removal of the two contaminants. Regeneration and reusability study showed that KCF is economically viable. Therefore, introducing inorganic particles like cobalt ferrite into the matrix of kaolinites provides a composite with promising adsorption capacity.

Sequestrating anionic and cationic dyes from wastewater using spray dried biopolymeric magnetic composite: Experimental and theoretical studies

Spray dried cross-linked chitosan/cobalt ferrite composite was synthesized and applied as an adsorbent for the removal of acid orange II and methylene blue. The composite was structurally, thermally, morphologically and magnetically characterized. The result obtained shows that the magnetic composite was in form of microspheres, while cobalt ferrite was encapsulated in the cross-linked chitosan with saturation magnetization of 10.79 emu g^-1. Adsorption studies revealed that acid orange II adsorbed more favorably on the composite than methylene blue. The adsorption process is spontaneous and exothermic. Liu isotherm model was found to be applicable for the adsorption process. Computational studies showed that the formation of hydrogen bond between acid orange II and the magnetic composite (at both acidic and alkaline pH) contributed to its better adsorption than methylene blue. Adsorption capacity of acid orange II at pH 3 and methylene blue at pH 12 are 542 and 173 mg g^-1 respectively at 303 K base on Liu isotherm model.