Megamerger of biosorbents and catalytic technologies for the removal of heavy metals from wastewater: Preparation, final disposal, mechanism and influencing factors

Heavy metal pollution, because of its high toxicity, non-biodegradability and biological enrichment, has been identified as a global aquatic ecosystems threat in recent decades. Due to the high efficiency, low cost, satisfactory recyclability, easy storage and separation, biosorbents have exhibited a promising prospect for heavy metals treatment in aqueous phase. This article comprehensively summarized different types of biosorbents derived from available low-cost raw materials such as agricultural and forestry wastes. The raw materials obtained are treated with conventional pretreatment or novel methods, which can greatly enhance the adsorption performance of the biosorbents. The suitable immobilization methods can not only further enhance the adsorption performance of the biosorbents, but also facilitate the process of separating the biosorbents from the wastewater. In addition, once biosorbents are put into large-scale use, the final disposal problems cannot be avoided. Therefore, it is necessary to review the currently accepted final disposal methods of biosorbents. Moreover, through the analysis of the adsorption and desorption mechanisms of biosorbents, it is not only beneficial to find the better methods to improve the adsorption performance of the biosorbents, but also better to explain the influencing factors of adsorption effect for biosorbents. Especially, different from many researches focused on biosorbents, this work highlighted the combination of biosorbents with catalytic technologies, which provided new ideas for the follow-up research direction of biosorbents. Finally, the purpose of this paper is to inject new impetus into the future development of biosorbents.

A green l-cysteine modified cellulose nanocrystals biosorbent for adsorption of mercury ions from aqueous solutions

Using a green biosorbent to remove toxic mercury ions from aqueous solutions is a significant undertaking. In the present study, a novel biosorbent, l-cysteine modified cellulose nanocrystals (Lcys-CNCs), was prepared by functionalizing high surface area cellulose nanocrystals with l-cysteine through periodate oxidation and reductive amination reaction. Lcys-CNCs were characterized by FT-IR, ¹³C CP-MAS NMR, elemental analysis, XPS, zeta potential and SEM. As cellulose nanocrystals are the natural nanomaterial, and l-cysteine contains strong mercury chelating groups, Lcys-CNCs show excellent adsorption capacity for mercury ions. The experimental conditions such as pH, contact time, and initial mercury ion concentration are discussed. The pseudo-second order model can describe the removal kinetics of Hg(ii) more accurately than the pseudo-first order model. The adsorption isotherm study of Hg(ii) followed the Langmuir model of monolayer adsorption. The maximum uptake capacity of Lcys-CNCs was determined to be 923 mg g⁻¹. Lcys-CNCs can remove mercury ions with 93% removal efficiency within 5 min from a 71 mg L⁻¹ solution. For Cd(ii), Pb(ii), Cu(ii) and Zn(ii) ions, Lcsy-CNCs can selectively adsorb Hg(ii) ions and the removal efficiency is 87.4% for Hg(ii). This study suggests Lcsy-CNCs are a green and highly efficient biosorbent for adsorption of mercury ions from aqueous solutions.

A green biosorbent, l-cysteine modified cellulose nanocrystals, was successfully synthesized and applied to adsorb mercury ions from aqueous solutions.

Bio-recycling of metals: Recycling of technical products using biological applications

The increasing demand of different essential metals as a consequence of the development of new technologies, especially in the so called "low carbon technologies" require the development of innovative technologies that enable an economic and environmentally friendly metal recovery from primary and secondary resources. There is serious concern that the demand of some critical elements might exceed the present supply within a few years, thus necessitating the development of novel strategies and technologies to meet the requirements of industry and society. Besides an improvement of exploitation and processing of ores, the more urgent issue of recycling of strategic metals has to be enforced. However, current recycling rates are very low due to the increasing complexity of products and the low content of certain critical elements, thus hindering an economic metal recovery. On the other hand, increasing environmental consciousness as well as limitations of classical methods require innovative recycling methodologies in order to enable a circular economy. Modern biotechnologies can contribute to solve some of the problems related to metal recycling. These approaches use natural properties of organisms, bio-compounds, and biomolecules to interact with minerals, materials, metals, or metal ions such as surface attachment, mineral dissolution, transformation, and metal complexation. Further, modern genetic approaches, e.g. realized by synthetic biology, enable the smart design of new chemicals. The article presents some recent developments in the fields of bioleaching, biosorption, bioreduction, and bioflotation, and their use for metal recovery from different waste materials. Currently only few of these developments are commercialized. Major limitations are high costs in comparison to conventional methods and low element selectivity. The article discusses future trends to overcome these barriers. Especially interdisciplinary approaches, the combination of different technologies, the inclusion of modern genetic methods, as well as the consideration of existing, yet unexplored natural resources will push innovations in these fields.

Highly selective and efficient adsorption of Hg2+ by a recyclable aminophosphonic acid functionalized polyacrylonitrile fiber

Mercury ions, even an ultra-trace amount in water, present a serious environmental concern. Hence, searching for cost-effective and high-performance Hg²⁺ adsorbents has acquired increasingly attention but still remained challenging. In this work, aminophosphonic acid was immobilized onto polyacrylonitrile fiber by chemical grafting approaches. The functionalized fiber (PAN_APF) possessed high adsorption selectivity and efficiency for Hg²⁺ when compared with other coexisting ions viz. Pb²⁺, Cd²⁺, Ag⁺, Zn²⁺, Cu²⁺, Ni²⁺, Co²⁺, Ca²⁺ and Mg²⁺. The adsorption results revealed that PAN_APF exhibited high removal capacities for Hg²⁺ over a wide pH range from 3 to 11. The adsorption process was better described by the pseudo second-order kinetic model, indicating the chemical interaction between Hg²⁺ and active groups on the PAN_APF. Moreover, the maximum adsorption capacity as calculated from the Langmuir adsorption model of 358mgg^-1 was higher than that of many other adsorbents. The PAN_APF could be reused more than 10 times and it is able to decrease Hg²⁺ below 50μgL^-1 which is the maximum discharge standard for mercury containing wastewater in China. A continuous-flow process was also implemented to remove Hg²⁺. The results suggested the environmentally friendly PAN_APF could be a promising candidate for Hg²⁺ removal in wastewater treatment.

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.

Surface modification of banana stem fibers via radiation induced grafting of poly(methacrylic acid) as an effective cation exchanger for Hg(ii)

A low cost adsorbent, banana stem fibers (BSFs), was used for modification by grafting with methacrylic acid via three free radical generation methods.

Modeling and optimization of Hg2+ ion biosorption by live yeast Yarrowia lipolytica 70562 from aqueous solutions under artificial neural network-genetic algorithm and response surface methodology: kinetic and equilibrium study

This study was devoted to the investigation of Hg²⁺ ion biosorption by a live yeast organism, namely, Yarrowia lipolytica 70562 (supplied commercially), which was sufficiently identified and studied by SEM-EDS and FT-IR methods.

Grape-like mesostructured silica nanoparticle-decorated single-walled carbon nanotubes: silica growth and dye adsorptivity

Single-walled carbon nanotube (SWCNT)-mesostructured silica nanoparticle (MSN) adsorbents (S-MSNs) were prepared through a simple one-step method with various loadings of SWCNTs.