NaOH-assisted H2O2 post-modification as a novel approach to enhance adsorption capacity of residual coffee waste biochars toward radioactive strontium: Experimental and theoretical studies

Alginate-collagen fibers composite biomass material for ultra-rapid recovery of strontium from contaminated water with excellent reusability

Recovering 90Sr from nuclear wastewater and nuclide-contaminated water not only avoids its potential environmental and health risks, but it can also be used for cancer treatment, manufacturing isotope batteries and environmental monitoring. A novel adsorbent material (OSA@CF/Zr) for ultra-fast recovery of Sr2+ was obtained by grafting oxidized sodium alginate on zirconium cross-linked collagen fibers. The OSA@CF/Zr demonstrated rapid adsorption of Sr²⁺, achieving a maximum capacity of 0.415 mmol g-¹ within 6 min. Even after 17 recycling cycles, it retained an adsorption capacity of approximately 0.26 mmol g-¹ , highlighting its superior reusability. The OSA@CF/Zr could be applied at pH of 4-10, were hardly affected by co-existing K+, Na+, and Cs+ ions, and the effects of Mg2+ and Ca2+ were easily masked by CDTA, exhibiting high selectivity for Sr2+. The OSA@CF/Zr was well suited for continuous column adsorption operation, and the amount of treated wastewater and the removal rate was almost independent of the flow rate. The adsorption column, containing 1 g of OSA@CF/Zr, successfully removed over 95 % of Sr2+ from 1.737 L of simulated surface water with an initial Sr2+ concentration of 7.886 mg L-1. OSA@CF/Zr is a very promising material for strontium recovery.

Transformer-based deep learning models for adsorption capacity prediction of heavy metal ions toward biochar-based adsorbents

Biochar adsorbents synthesized from food and agricultural wastes are commonly applied to eliminate heavy metal (HM) ions from wastewater. However, biochar's diverse characteristics and varied experimental conditions make the accurate estimation of their adsorption capacity (qe) challenging. Herein, various machine-learning (ML) and three deep learning (DL) models were built using 1518 data points to predict the qe of HM on various biochars. The recursive feature elimination technique with 28 inputs suggested that 14 inputs were significant for model building. FT-transformer with the highest test R2 (0.98) and lowest root mean square error (RMSE) (0.296) and mean absolute error (MAE) (0.145) outperformed various ML and DL models. The SHAP feature importance analysis of the FT-transformer model predicted that the adsorption conditions (72.12%) were more important than the pyrolysis conditions (25.73%), elemental composition (1.39%), and biochar's physical properties (0.73%). The two-feature SHAP analysis proposed the optimized process conditions including adsorbent loading of 0.25 g, initial concentration of 12 mg/L, and solution pH of 9 using phosphoric-acid pre-treated biochar synthesized from banana-peel with a higher O/C ratio. The t-SNE technique was applied to transform the 14-input matrix of the FT-Transformer into two-dimensional data. Finally, we outlined the study's environmental implications.

From Waste to Resource: Valorization of Lignocellulosic Agri-Food Residues through Engineered Hydrochar and Biochar for Environmental and Clean Energy Applications-A Comprehensive Review

Agri-food residues or by-products have increased their contribution to the global tally of unsustainably generated waste. These residues, characterized by their inherent physicochemical properties and rich in lignocellulosic composition, are progressively being recognized as valuable products that align with the principles of zero waste and circular economy advocated for by different government entities. Consequently, they are utilized as raw materials in other industrial sectors, such as the notable case of environmental remediation. This review highlights the substantial potential of thermochemical valorized agri-food residues, transformed into biochar and hydrochar, as versatile adsorbents in wastewater treatment and as promising alternatives in various environmental and energy-related applications. These materials, with their enhanced properties achieved through tailored engineering techniques, offer competent solutions with cost-effective and satisfactory results in applications in various environmental contexts such as removing pollutants from wastewater or green energy generation. This sustainable approach not only addresses environmental concerns but also paves the way for a more eco-friendly and resource-efficient future, making it an exciting prospect for diverse applications.

Enhanced selectivity and recovery of phosphate and nitrate ions onto coffee ground waste biochars via co-precipitation of Mg/Al layered double hydroxides: A potential slow-release fertilizer

In this study, the feasibility of Mg/Al layered double hydroxides (LDH) functionalized coffee ground waste biochars (LDHMgAl@CWGB) as a potential adsorbent to selectively recover phosphate (PO43-) and nitrate (NO3-) ions in aqueous phases and their consecutive uses as a slow-release fertilizer for stimulating the plant growth were identified. The higher adsorption capacity of PO43- and NO3- ions by LDHMgAl@CWGB (PO43- = 6.98 mgP/g, NO3- = 2.82 mgN/g) compared with pristine coffee ground waste biochars (CWGB; PO43- = 0.19 mgP/g, NO3- = 0.32 mgN/g) was mainly due to the incorporation of Mg/Al mixed oxides and Cl contents. Chemisorption and intra-particle mainly controlled the adsorptive recovery of PO43- and NO3- ions by CWGB and LDHMgAl@CWGB in aqueous phases and their adsorption toward CWGB and LDHMgAl@CWGB proceeded endothermically and spontaneously. The changes in the major adsorption mechanisms of PO43- and NO3- ions from ligand exchange (CWGB) to electrostatic surface complexation and anion-exchange (LDHMgAl@CWGB) supported the conclusion that the alternation of the surface features through Mg/Al LDH functionalization might improve selectivity and adsorption capacity of PO43- and NO3- ions onto CWGB under the co-existence of Cl-, SO42-, and HCO3- ions. Since PO43-- and NO3--loaded LDHMgAl@CWGB exhibited much higher seed germination, root and shoot growth rates of garden cress seeds (Lepidium sativum L) than other liquid and solid matrices, including 5 mgP/L PO43- and 5 mgN/L NO3-, 10 mgP/L PO43- and 10 mgN/L NO3-, and LDHMgAl@CWGB, it can be postulated that PO43-- and NO3--loaded LDHMgAl@CWGB could be practically applicable to the agricultural field as a slow-release fertilizer to facilitate the seed germination, root and shoot growth of the plants.

Functionalization of pine sawdust biochars with Mg/Al layered double hydroxides to enhance adsorption capacity of synthetic azo dyes: Adsorption mechanisms and reusability

This study determined that the adsorption of azo dyes, Methyl Orange (MO) and Sunset Yellow FCF (SYF), using the pristine pine sawdust biochar (PSB) and post-modified PSB with Mg/Al layered double hydroxides (PSB-LDH_MgAl) was examined to offer valuable information into the differences in their adsorption mechanisms. Although a lower specific surface area of PSB-LDH_MgAl (147.2 m² g^-1) than PSB (495.7 m² g^-1), LDH_MgAl were successfully functionalized on the PSB surface through co-precipitation, which was highly related to the improvements of adsorption capacity of PSB-LDH_MgAl toward MO and SYF. The MO and SYF adsorption kinetics by PSB and PSB-LDH_MgAl were confirmed to the pseudo-second-order and considered chemisorption. The adsorption capacity of MO and SYF adsorbed onto PSB-LDH_MgAl (MO = 21.8 mg g^-1, SYF = 23.6 mg g^-1) were significantly higher than that of PSB (MO = 2.2 mg g^-1, SYF = 1.6 mg g^-1). The adsorption isotherms of MO and SYF by PSB were well fitted by Freundlich isotherm, whereas the MO and SYF via PSB-LDH_MgAl were by Langmuir isotherm. Even after 3 adsorption-desorption cycles using desorbents, the PSB-LDH_MgAl remained excellent reusability (reuse efficiency: >81.2%). These findings suggest that post-modification with LDH_MgAl might accelerate the adsorption performance (i.e., electrostatic interaction) of azo dyes to PSB in water.