Boosting Fenton's Oxidation Reaction by a Food Waste-Derived Catalyst for Oxidizing Organic Dyes: Synergistic Effect of Complex Iron Oxides and the Layer Carbon Structure

The constant increase in the human population drives the demand for food supply and thereby increasing the food wastage dramatically all over the world. Especially, around 60% of banana biomass has been generated as inedible domestic waste. Herein, we successfully employed banana waste as a catalyst for Fenton's oxidation reaction. The biomass-derived catalysts were subjected to various characterization techniques such as XRD, ATR-FTIR, confocal Raman spectroscopy, and XPS, XRF, BET, SEM, and TEM analyses. The XRD results revealed that, after carbonization of the dried banana bract material, a perloffite-like metal oxide phase was formed due to the aerial oxidation reaction. Characterization results of Raman and ATR-FTIR confirm that the carbonized catalyst possesses a layer-like structure with different types of functional groups. The calcium, magnesium, potassium, sodium, and iron are the dominating metal species in the resultant material, which was evident from the XRF and EDAX analyses. The carbonized banana bract catalyst is successfully utilized for the Fenton's oxidation reaction at neutral pH. The experimental results showed that the degradation efficiency of the fresh catalyst was 95% in 4 h of reaction time, and the stability of the catalyst was retained up to nine consecutive cycles. The high activity of MB, methylene blue, is mainly attributed to the strong interaction between oxy functional groups of the catalyst and MB molecule as compared to RhB. Further, the calculated efficiency of the hydrogen peroxide was found to be 99% and the self-decomposition of hydrogen peroxide by the formed metal oxides was highly limited.

Synthesis of Metakaolin Based Alkali Activated Materials as an Adsorbent at Different Na2SiO3/NaOH Ratios and Exposing Temperatures for Cu2+ Removal

Water contamination is a major issue due to industrial releases of hazardous heavy metals. Copper ions are among the most dangerous heavy metals owing to their carcinogenicity and harmful effects on the environment and human health. Adsorption of copper ions using alkali activated materials synthesized through the polycondensation reaction of an alkali source and aluminosilicates is the most promising technique, and has a high adsorption capability owing to a large surface area and pore volume. This research focuses on the effect of the alkaline activator ratio, which is a sodium silicate to sodium hydroxide ratio. Various exposing temperatures on metakaolin based alkali activated materials on a surface structure with excellent functional properties can be used as adsorbent materials for the removal of copper ions. A variety of mix designs were created with varying sodium silicate to sodium hydroxide ratios, with a fixed sodium hydroxide molarity, metakaolin to alkali activator ratio, hydrogen peroxide, and surfactant content of 10 M, 0.8, 1.00 wt%, and 3.0 wt%, respectively. Most wastewater adsorbents need high sintering temperatures, requiring an energy-intensive and time-consuming manufacturing process. In this way, metakaolin-based alkali activated materials are adsorbent and may be produced easily by solidifying the sample at 60 °C without using much energy. The specific surface area, water absorption, microstructure, phase analysis, functional group analysis, and adsorption capability of copper ions by metakaolin based alkali activated materials as adsorbents were evaluated. The water absorption test on the samples revealed that the sodium silicate to sodium hydroxide 0.5 ratio had the highest water absorption percentage of 36.24%, superior pore size distribution, and homogeneous porosity at 60 °C, with a surface area of 24.6076 m²/g and the highest copper ion uptake of 63.726 mg/g with 95.59% copper ion removal efficiency at adsorption condition of pH = 5, a dosage of 0.15 g, 100 mg/L of the initial copper solution, the temperature of 25 °C, and contact time of 60 min. It is concluded that self-supported metakaolin based alkali activated material adsorbents synthesized at low temperatures effectively remove copper ions in aqueous solutions, making them an excellent alternative for wastewater treatment applications.

A potential lignocellulosic biomass based on banana waste for critical rare earths recovery from aqueous solutions

Rare earth elements (REE) present multiple applications in technological devices but also drawbacks (scarcity and water contaminant). The current study aims to valorise the banana wastes - banana rachis (BR), banana pseudo-stem (BPS) and banana peel (BP) as sustainable adsorbent materials for the recovery of REE (Nd³⁺, Eu³⁺, Y³⁺, Dy³⁺ and Tb³⁺). The adsorbent materials were characterized using analytical techniques such as: Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, zeta potential and scanning electron microscopy with energy dispersive X-ray probe. The adsorption performance and mechanisms were studied by pH dependence, equilibrium isotherms, kinetics, thermodynamics, ion-exchange and desorption evaluation. The results show good adsorption capacities for the three materials, highlighting BR that presents ∼100 mg/g for most of the REE. The adsorption process (100 mg REE/L) reaches the 60% uptake in 8 min and the equilibrium within 50 min. On the other hand, the thermodynamic study indicates that the adsorption is spontaneous and exothermic (ΔH° < 40 kJ/mol). The adsorption mechanism is based on the presence of carboxylic groups that induce electrostatic interactions and facilitate the surface nucleation of REE microcrystals coupled to an ion exchange process as well as the presence of other oxygen containing groups that establish weak intermolecular forces. The recovery of REE from the adsorbent (∼97%) is achieved using EDTA as desorbing solution. This research indicates that banana waste and particularly BR is a new and promising renewable bioresource to recover REE with high adsorption capacity and moderated processing cost.

Sodium dodecyl sulfate-coated-cationized agroforestry residue as adsorbent for benzene-adsorptive sequestration from aqueous solution

The aim of this work is to convert agroforestry residue to a novel adsorbent (M-1CTA-SDS-BT) used for adsorptive benzene sequestration from aqueous solution. In this study, the anionic surfactant-coated-cationized banana trunk was synthesized and characterized for batch adsorption of benzene from aqueous solution. The surface morphology, surface chemistry, surface area, and pore properties of the synthesized adsorbents were examined. It was proven that surface cationization successfully increased the benzene adsorption capacity of sodium dodecyl sulfate-coated adsorbents. The Langmuir isotherm model satisfactorily described the equilibrium adsorption data. The maximum benzene adsorption capacity (q_max) of 468.19 μmol/g was attained. The kinetic data followed the pseudo-second-order kinetic model in which the rate-limiting step was proven to be the film diffusion. The batch-adsorbent regeneration results indicated that the M-1CTA-SDS-BT could withstand at least five adsorption/desorption cycles without drastic adsorption capacity reduction. The findings demonstrated the adsorptive potential of agroforestry-based adsorbent as a natural and cheap material for benzene removal from contaminated water.

Biomass Modification Using Cationic Surfactant Cetyltrimethylammonium Bromide (CTAB) to Remove Palm-Based Cooking Oil

Adsorption based on natural fibre seems to widely used for oily wastewater recovery due to its low cost, simplicity, feasibility, easy handling, and effectiveness. However, oil sorbent based on natural fibre without modification has low adsorption capacity and selectivity. Thus, this paper proposes chemical modification of sago hampas to improve its adsorbent efficiency for the removal of palm-based cooking oil. The chemical modification was performed using a cationic surfactant, cetyltrimethylammonium bromide (CTAB). The chemical and surface properties of both unmodified and modified sago hampas were characterized by Fourier-Transform Infrared (FTIR) and Scanning Electron Microscopy (SEM). Parameters studied for the removal of cooking oil using modified sago hampas were sorption time, adsorbent dosage, and initial pH. The removal capacity was also compared using unmodified sago hampas. The results showed that additional functional groups were introduced on the surface of modified sago hampas. Modified sago hampas also showed a greater porosity than unmodified sago hampas. These properties enhanced the adsorption of palm-based cooking oil onto the surface of modified sago hampas. Modified sago hampas shows better removal of palm-based cooking oil than unmodified sago hampas, where 84.82% and 68.08% removal were achieved by modified and unmodified sago hampas, respectively. The optimum adsorption of palm-based cooking oil was identified at 45 min sorption time, pH 2, and 0.2 g adsorbent dosage.

Prospects of banana waste utilization in wastewater treatment: A review

This review article explores utilization of banana waste (fruit peels, pseudo-stem, trunks, and leaves) as precursor materials to produce an adsorbent, and its application against environmental pollutants such as heavy metals, dyes, organic pollutants, pesticides, and various other gaseous pollutants. In recent past, quite a good number of research articles have been published on the utilization of low-cost adsorbents derived from biomass wastes. The literature survey on banana waste derived adsorbents shown that due to the abundance of banana waste worldwide, it also considered as low-cost adsorbents with promising future application against various environmental pollutants. Furthermore, raw banana biomass can be chemically modified to prepare efficient adsorbent as per requirement; chemical surface functional group modification may enhance the multiple uses of the adsorbent with industrial standard. It was evident from a literature survey that banana waste derived adsorbents have significant removal efficiency against various pollutants. Most of the published articles on banana waste derived adsorbents have been discussed critically, and the conclusion is drawn based on the results reported. Some results with poorly performed experiments were also discussed and pointed out their lacking in reporting. Based on literature survey, the future research prospect on banana wastes has a significant impact on upcoming research strategy.