Preparation of new diatomite-chitosan composite materials and their adsorption properties and mechanism of Hg(II)

Graphene-magnetite functionalized diatomite for efficient removal of organochlorine pesticides from aquatic environment

A unique composite based on graphene oxide, magnetite, and diatomite was synthetized by eco-friendly dry coating technique for the removal of four toxic organochlorine pesticides from agricultural drainage. The prepared composite was fully characterized using X-ray fluorescence (XRF), X-ray diffraction (XRD), particle size analyzer, Vibrating-sample magnetometer (VSM), magnetic susceptibility meter, zeta potential, scanning electron microscopy-energy dispersive X-ray spectrometer (SEM-EDS), and Brunauer-Emmett-Teller analysis (BET) techniques. The characterization results confirmed the fabrication of a discrete core/shell structured composite possess both adsorptive and magnetic nature. The surface area, pore volume and pore diameter were 23.4 m²/g, 0.0026 cm³/g, and 4.5 nm, respectively. The amenability to use the fabricated composite as an adsorbent for some organochlorine pesticides was investigated under different conditions of concentration, time, pH, and temperature. Batch adsorption experiment showed that 97% removal efficiency was observed for all the studied pesticides with adsorption capacities of 7.78 mg/g after 2 h contact time and at any pH region. The adsorption was exothermic (ΔH < 0), spontaneous (ΔG° < 0), followed pseudo 2nd order kinetics (R² > 0.998), and fitted well to Langmuir's isotherm pattern for all pesticides (R² > 0.98). It is assumed that organochlorine pesticides were initially physisorbed by the graphene nanoplatelets via hydrophobic and π-π interactions along with chemisorption for forming monolayer. Moreover, the pesticides molecules could diffuse in the DMG composite micropores and be trapped in the structural defects. The regeneration of the composite exhibited over 90% removal efficiency even after seven cycles. The fabricated composite was examined to remove organochlorine from a real water sample, the obtained results suggest the possibility to use this composite as an economical, effective and sustainable adsorbent for the treatment of pesticides contaminating water.

Single and Binary Adsorption Systems of Rhodamine B and Methylene Blue onto Alkali-Activated Vietnamese Diatomite

Diatomite was slightly modified with a sodium hydroxide solution. The resulting material was characterized by using energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and nitrogen adsorption-desorption isotherms. The so-treated diatomite has a high specific surface area (77.8 m2/g) and a high concentration of isolated silanol groups on the surface, and therefore, its adsorption capacity increases drastically in both the single and binary adsorption systems for rhodamine B and methylene blue. The binary system is more effective than the single system, with methylene blue being adsorbed more than rhodamine B. The adsorption process is spontaneous and fits well with the Langmuir isothermal model, and it depends on pH significantly.

Synthesis of Nano-Magnetite from Industrial Mill Chips for the Application of Boron Removal: Characterization and Adsorption Efficacy

The present study synthesized nano-magnetite (Fe3O4) from milled steel chips using the high energy ball milling (HEBM) method, characterized it, and then utilized it as a sorbent to remediate boron concentration at various pH (4-9), dosages (0.1-0.5 g), contact times (20-240 min), and initial concentrations (10-100 mg/L). The nano-sorbents were characterized based on SEM structure, elemental composition (EDX), surface area analysis (BET), crystallinity (XRD), and functional group analysis (FTIR). The highest adsorption capacity of 8.44 mg/g with removal efficiency of 84% was attained at pH 8, 0.5 g dosage, contact time of 180 min, and 50 mg/L initial concentration. The experimental data fit best with the pseudo-second-order kinetic model with R2 of 0.998, while the Freundlich adsorption isotherm describes the adsorption process with an R2 value of 0.9464. A regeneration efficiency of 47% was attained even after five cycles of reusability studies. This efficiency implies that the nano-magnetite has the potential for sustainable industrial application.

Chitosan-MnO2 nanocomposite for effective removal of Cr (VI) from aqueous solution

In this report, the adsorption of Cr(VI) onto MnO₂/CS nanocomposite material from aqueous solution is investigated. All the factors, which affect the adsorption, such as pH, adsorption time, Cr(VI) initial concentration and adsorbent dosage, are also examined. The results obtained show that the Cr(VI) uptake is strongly affected by pH and ion strength. Analysis within the nonlinear isotherm models indicates that the Sips isotherm combining with the Langmuir and Freundlich models offer the best fit to the experimental data due to the obtained highest R² and smallest RMSE and χ² values. The calculated Langmuir monolayer adsorption capacity is 61.56 mg g^-1 at pH of 2.0 and adsorption time of 120 min. Moreover, the mechanism studies by combining theoretical models with analytical spectroscopies reveal that the electrostatic attraction plays the important role to the uptake of Cr(VI) onto MnO₂/CS nanocomposite. Therefore, the present nanocomposite material can be applied to remove total Cr from wastewater produced by the galvanized manufacturing factory with a relatively high efficiency.

Fabrication of Green Diatomite/Chitosan-Based Hybrid Foams with Dye Sorption Capacity

The latest tendency of the scientific community regards the development of different classes of green materials able to solve pollution problems caused by industrial and human activity. In this paper, chitosan and diatomite were used to produce a broad-spectrum hybrid adsorbent, either in powder or in monolithic form for environmental pollutant removal. Diatomite-chitosan-based powders and porous diatomite-chitosan hybrids were prepared and characterized by chemical-physical, thermal and morphological analysis. Moreover, their adsorbent capacity towards anionic dye (Indigo Carmine) was also evaluated. Obtained data showed that chitosan improves the adsorption capacity of both systems, increasing the uptake of dye in both diatomite-chitosan systems.

Naturally available diatomite and their surface modification for the removal of hazardous dye and metal ions: A review

The presence of toxic pollutants such as dyes and metal ions at higher concentrations in water is very harmful to the environment. Removal of these pollutants using diatomaceous earth or diatomite (DE) and surface-modified DE has been extensively explored due to their excellent physio-chemical properties and low cost. Therefore, naturally available DE being inexpensive, their surface modified adsorbents could be one of the potential candidates for the wastewater treatment in the future. In this context, the current review has been summarized for the removal of both pollutants i.e., dyes and metal ions by surface-modified DE using the facile adsorption process. In addition, this review is prominently focused on the various modification process of DE, their cost-effectiveness; the physio-chemical characteristics and their maximum adsorption capacity. Further, real-time scenarios of reported adsorbents were tabulated based on the cost of the process along with the adsorption capacity of these adsorbents.

Chitosan/MCM-48 nanocomposite as a potential adsorbent for removing phenol from aqueous solution

A new hybrid mesoporous nanocomposite (CMCM-48) based on chitosan and silica MCM-48 was considered as a potential adsorbent for removing phenol from aqueous solutions (toxic liquid waste) in a batch process. The new composite adsorbent was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and nitrogen adsorption–desorption isotherms. The adsorption isotherm studies were analyzed using linear and nonlinear Langmuir, Freundlich and Dubinin–Radushkevich models for the optimum conditions when the initial phenol concentration, pH, adsorption temperature and time were 10–500 mg L⁻¹, 3–10, 25.5 °C and 300 min, respectively. It was revealed that the experimental results agree well with the Dubinin–Radushkevich model, i.e. the correlation coefficient R² was 0.983085. The adsorption kinetics was modeled with linear and nonlinear pseudo-first-order, pseudo-second-order and intra particle diffusion kinetic models. The pseudo-second-order model was the best for describing the adsorption process with a correlation coefficient R² = 0.99925. The stability of the equilibrium data was studied for a phenol sorbent with a maximum adsorption capacity of 149.25 mg g⁻¹. The results verified that the synthesized CMCM-48 was an efficient adsorbent for removing phenol from aqueous solutions.

A new hybrid mesoporous nanocomposite (CMCM-48) based on chitosan and silica MCM-48 was considered as a potential adsorbent for removing phenol from aqueous solutions (toxic liquid waste) in a batch process.

Preparation of chitosan/MCM-41-PAA nanocomposites and the adsorption behaviour of Hg(II) ions

A novel functional hybrid mesoporous composite material (CMP) based on chitosan and MCM-41-PAA was reported and its application as an excellent adsorbent for Hg(II) ions was also investigated. Innovatively, MCM-41-PAA was prepared by using diatomite and polyacrylic acid (PAA) with integrated polymer-silica hybrid frameworks, and then CMP was fabricated by introducing MCM-41-PAA to chitosan using glutaraldehyde as a cross-linking agent. The structure and morphology of CMP were characterized by X-ray diffraction, Fourier transform infrared spectra, thermogravimetric analysis, scanning electron microscopy and Brunauer-Emmett-Teller measurements. The results showed that the CMP possessed multifunctional groups such as -OH, -COOH and -NH₂ with large specific surface area. Adsorption behaviour of Hg(II) ions onto CMP was fitted better by the pseudo-second-order kinetic model and the Langmuir model when the initial Hg(II) concentration, pH, adsorption temperature and time were 200 mg l^-1, 4, 298 K and 120 min, respectively, as the optimum conditions. The corresponding maximum adsorption capacity could reach 164 mg g^-1. According to the thermodynamic parameters determined such as free energy, enthalpy and entropy, the adsorption process of Hg(II) ions was spontaneous endothermic adsorption.