Adsorptive removal of direct red 80 and methylene blue from aqueous solution by potato peels: a comparison of anionic and cationic dyes

Aging and characterization of disposable polypropylene plastic cups based microplastics and its adsorption for methylene blue

Microplastics (MPs) as emerging pollutants are of increasing concern, due to their ubiquitous, uncertain, and complex environmental impacts. Different from the standard spherical MPs without additives, here polypropylene microplastics (PP-MPs) in flake derived from the disposable plastic cup in food-grade in daily life were studied. The characterization of PP-MPs demonstrated that the carbonyl index represented the aging degree was enhanced from 0.26 significantly to 0.82 after 10 days, and the aging process fitted well with pseudo-first-order kinetic. Moreover, the crystallinity degree, polarity and surface negative charges were enhanced, while the hydrophobicity was decreased. The adsorption behavior of PP-MPs toward methylene blue (MB), and the impacts of various pHs, salinities, and humic acid in aquatic environments were also explored. The pseudo-second-order kinetic, Henry and Sips isotherm models provided a good correlation with the experimental data, indicating that the rate-limiting step was closely related with the complex surface adsorption, and the hydrophobic partitioning, polar interaction, electrostatic attraction, and hydrogen bonding were possibly involved in the adsorption. These exhaustive experiments aim to provide a theoretical basis for assessing and better understanding the environmental behavior of disposable PP plastic cups in nature.

Cationic oxides and dioxides of modified sugarcane bagasse beads with applications as low-cost sorbents for direct red 28 dye

The direct red 28 (DR28) dye contamination in wastewater blocks the transmission of light into the water body resulting in the inability to photosynthesize by aquatic life. In addition, it is difficult to break down and persist in the environment, and it is also harmful to aquatic life and water quality because of its aromatic structure. Thus, wastewater contaminated with dyes is required to treat before releasing into the water body. Sugarcane bagasse beads (SBB), sugarcane bagasse modified with titanium dioxide beads (SBBT), sugarcane bagasse modified with magnesium oxide beads (SBBM), sugarcane bagasse modified with aluminum oxide beads (SBBA), and sugarcane bagasse modified with zinc oxide beads (SBBZ) for DR28 dye removal in aqueous solution, and they were characterized with several techniques of BET, FESEM-FIB, EDX, FT-IR, and the point of zero charges (pHpzc). Their DR28 dye removal efficiencies were examined through batch tests, adsorption isotherms, and kinetics. SBBM had the highest specific surface area and pore volume, whereas its pore size was the smallest among other materials. The surfaces of SBB, SBBM, SBBT, and SBBA were scaly sheet surfaces with an irregular shape, whereas SBBZ was a coarse surface. Oxygen, carbon, calcium, chloride, sodium, O-H, C-H, C=O, C=C, and C-O-C were found in all materials. The pHpzc of SBB, SBBT, SBBM, SBBA, and SBBZ were 6.57, 7.31, 10.11, 7.25, and 7.77. All materials could adsorb DR28 dye at 50 mg/L by more than 81%, and SBBM had the highest DR28 dye removal efficiency of 94.27%. Langmuir model was an appropriate model for SBB, whereas Freundlich model was a suitable model for other materials. A pseudo-second-order kinetic model well described their adsorption mechanisms. Their adsorptions of the DR28 dye were endothermic and spontaneous. Therefore, they were potential materials for adsorbing DR28 dye, especially SBBM.

Kinetic studies and conditions optimizations for the removal of direct red 80 dye from wastewater using cotton calyx and iron oxide composite

This study focusses on the adsorption efficiency of cotton pod (Gossypium arboreum) for biosorption of direct red (DR) 80 dye. The effect of dye concentration, pH, shaking time, adsorbent dose and temperature was considered to evaluate the adsorption efficiency of the cheapest raw material on the removal of dye. Various concentrations (10–50 ppm) were examined and maximum percentage removal of the adsorbent was obtained at pH 1 with adsorbent dose of 0.9 g and shaking time of 60 min. To enhance the adsorption efficiency of the adsorbent, the cotton calyx was treated with FeSO4.7H2O and investigated the removal of the raw adsorbent and the composite. It was examined that the removal efficiency of the composite is more than that of raw adsorbent. The composite was more efficient as dye removal reached up to 97%. FTIR of the composite shows an additional peak at 650 cm−1 for presence of Fe-O group and confirmation of composite formation. SEM micrograph showed that the particles in composite are more packed compared to the raw adsorbent. Mathematical models were applied and kinetic studies also have been done to provide better results regarding to the experimental data. It is concluded that the prepared adsorbent could be used as a tool for the removal of toxic pollutants from textile wastewater.