Removal of Copper Ions and Methylene Blue from Aqueous Solution Using Chemically Modified Mixed Hardwoods Powder as a Biosorbent

Co-production of spirosiloxane and biochar adsorbent from wheat straw by a low-cost and environment-friendly method

To enhance the value of wheat straw derivatives, wheat straw ash (WSA) was used as a reactant for the first time to synthesize spirocyclic alkoxysilane, an important organosilicon raw material, using an energy-saving and environmentally friendly non-carbon thermal reduction method. After spirocyclic alkoxysilane extraction, the biochar in the wheat straw ash prepared an adsorbent for Cu²⁺. The maximum copper ion adsorption capacity (Q_m) of silica-depleted wheat straw ash (SDWSA) was 31.431nullmg/g, far exceeding those of WSA and similar biomass adsorbents. The effects of the pH, adsorbent dose, and contact time on the adsorption behaviour of the SDWSA for Cu²⁺ adsorption were systematically investigated. The adsorption mechanism of Cu²⁺ by the SDWSA was investigated using the Langmuir, Freundlich, pseudo-first-order kinetic, pseudo-second-order kinetic, and Weber and Morris models by combining the preliminary experimental data and characterization results. The adsorption isotherm and Langmuir equation matched perfectly. The Weber and Morris model can describe the mass-transfer mechanism of Cu²⁺ adsorption by SDWSA. Both film and intraparticle diffusion are rapid control steps. Compared to WSA, SDWSA has a larger specific surface area and a higher content of oxygen-containing functional groups. A large specific surface area provides more adsorption sites. Oxygen-containing functional groups react with Cu²⁺ through electrostatic interactions, surface complexation, and ion exchange, which are the possible adsorption mechanisms for SDWSA. These methods improve the added value of wheat straw derivatives and promote wheat straw ash recovery and centralized treatment. This makes it possible to use the thermal energy of wheat straw and facilitates the treatment of exhaust gases and carbon capture.

Enhanced characteristics and mechanism of Cu(II) removal from aqueous solutions in electrocatalytic internal micro-electrolysis fluidized-bed

For the purification of heavy metal wastewater, internal micro-electrolysis (IME) was considered as an effective method but some disadvantage greatly restricts its application. Electrocatalytic internal micro-electrolysis (ECIME) fluidized bed using iron-carbon particles was proposed to avoid disadvantaging of IME. The principal aim of this study was to investigate the enhanced removal characteristics, mechanism, and kinetic behavior of Cu(II) that none clear before. ECIME reactor shows a better copper removal performance and depends much on the polarization of the external electric field (EEF). Both the reaction rate and removal efficiency of copper electrodeposition improved obviously. Noteworthy is more than 88.0% of Cu(II) in aqueous solutions was removed by enhanced electrodeposition, and only about 10.0% of Cu(II) was absorbed and flocculated through the in situ formed iron hydroxyl compounds. Through scanning electron microscopy (SEM) and electrochemical analysis, copper can effectively electrodeposition on the surface of iron-carbon particles in ECIME reactor and accordingly the enhanced mechanisms were proposed. 1) Iron-carbon particles of ECIME formation of microelectrodes with high surface potential, larger specific area, and active sites through electrode collision and repolarization. 2) Copper electrodeposition on the formed microelectrodes exhibited greater reduction peak potential, reaction overpotential and exchange current density, which influenced by the polarization voltage significantly. 3) The electrocatalytic environment tend to in situ generate iron polymer hydroxyl compounds help to further remove residual Cu(II). ECIME fluidized-bed has promised potential for heavy metal containing wastewater purification and metal recovery. In addition, the proposed reaction models will be useful for field application.

Optimization and Characterization of Wheat Bran Modified by Citric Acid Using a Dry Reaction Method for Enhancement of Methylene Blue Adsorption

Wheat bran is modified thermochemically through reaction with citric acid, as carboxyl groups bearing agent, according to a dry condition method at the elevated temperature. In this study, the main objectives are optimization the factors affecting on the pendant carboxylic acid groups of wheat bran–citrate, including concentration of citric acid solution (0–1.8 M), volume of citric acid solution (5.4–16.2 g), curing temperature (0–170 °C), curing time (0–90 min.), mixing method (solution mixing vs kneading) of reactants, and the catalyst effect (0–5, sodium phosphate dibasic dodecahydrate/citric acid molar ratio). The amount of pendant carboxylic acid groups is determined by simple acid-base titration. The obtained methylene blue adsorption data is well matched with the amount of pendant carboxylic acid groups in wheat bran–citrate and this amount increase with an increase in pendant carboxylic acid groups.

Anisotropic polydopamine capsules with an ellipsoidal shape that can tolerate harsh conditions: efficient adsorbents for organic dyes and precursors for ellipsoidal hollow carbon particles

Ellipsoidal PDA capsules with enhanced mechanical rigidity can be directly carbonized into ellipsoidal carbon capsules and used as efficient adsorbents for organic dyes in water.

Biosorption of methylene blue from wastewater by an extraction residue of Salvia miltiorrhiza Bge

Efforts were made in this study to using an extraction residue of Salvia mitiorrziza Bge (SM), a widely utilized traditional Chinese medicine, as an effective biosorbent of methylene blue from polluted water. Batch experiments were carried out with original and chemical modification, particle size, dosage, solution pH, contact time, and initial concentration of the dye. Experimental data fit Langmuir isotherm and pseudo-second order kinetic best compared to other models applied in the study. Characterization of adsorption was determined by FT-IR, SEM and particle surface area measurement. The maximum monolayer biosorption capacity of raw SM is 100.0mg·g(-1). The citric acid and Na2CO3 modification can significantly enhance this value up to 161.29 and 178.57mg·g(-1), respectively. This investigation provides a novel approach for reutilizing the enormous quantity of Chinese herbal medicine wastes, which is significant since these dregs have brought out big environmental and heathy problems in the present China.

Potential biosorbent derived from Calligonum polygonoides for removal of methylene blue dye from aqueous solution

The ash of C. polygonoides (locally called balanza) was collected from Lakki Marwat, Khyber Pakhtunkhwa, Pakistan, and was utilized as biosorbent for methylene blue (MB) removal from aqueous solution. The ash was used as biosorbent without any physical or chemical treatment. The biosorbent was characterized by using various techniques such as Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The particle size and surface area were measured using particle size analyzer and Brunauer-Emmett-Teller equation (BET), respectively. The SEM and BET results expressed that the adsorbent has porous nature. Effects of various conditions such as initial concentration of methylene blue (MB), initial pH, contact time, dosage of biosorbent, and stirring rate were also investigated for the adsorption process. The rate of the adsorption of MB on biomass sample was fast, and equilibrium has been achieved within 1 hour. The kinetics of MB adsorption on biosorbent was studied by pseudo-first- and pseudo-second-order kinetic models and the pseudo-second-order has better mathematical fit with correlation coefficient value (R²) of 0.999. The study revealed that C. polygonoides ash proved to be an effective, alternative, inexpensive, and environmentally benign biosorbent for MB removal from aqueous solution.