Effect of multi-walled carbon nanotubes on extractability of Sb and Cd in contaminated soil

Research progress of applications for nano-materials in improved QuEChERS method

The quick, easy, cheap, effective, rugged, and safe (QuEChERS) approach is widely used in sample pretreatment in agricultural products, food, environment, etc. And nano-materials are widely used in QuEChERS method due to its small size and large specific surface area. In this review, we examine the typical applications of several commonly used nano-materials in improved QuEChERS method. These materials include multi-walled carbon nanotubes (MWCNTs) and their derivatives, magnetic nanoparticles (MNPs), metal organic frameworks (MOFs), covalent organic frameworks (COFs), graphene oxide (GO), lipid and protein adsorbent (LPAS), cucurbituril (CBs), and carbon nano-cages (CNCs), and so on. The strengths and weaknesses of each nano-material are presented, as well as the challenging aspects that need to be addressed in future research. By comparing the applications and the current technology development, this review suggests utilizing artificial intelligence (AI) to screen suitable combinations of purification agents and performing virtual simulation experiments to verify the reliability of this methodology. By doing so, we aim to accelerate the development of new products and decrease the cost of innovation. It also recommends designing smarter pretreatment instruments to enhance the convenience and automation of the sample pretreatment process and reduce the margin for human error.

Unraveling the role of multi-walled carbon nanotubes in a corn-soil system: Plant growth, oxidative stress and heavy metal(loid)s behavior

In the age of nanotechnological advancement, carbon nanotubes (CNTs) are drawing global attention. However, few studies have been published on the crop growth responses to CNTs in heavy metal(loid)s contaminated environments. A pot experiment was conducted to assess the effect of multi-walled carbon nanotubes (MWCNTs) on plant development, oxidative stress, and heavy metal(loid)s behavior in a corn-soil system. Corn (Zea mays L.) seedlings were cultivated in soil containing Cadmium (Cd) and Arsenic (As) that had been primed with 0, 100, 500, and 1000 mg kg^-1 MWCNTs. The application of 100 and 500 mg kg^-1 MWCNTs improved shoot length by 6.45% and 9.21% after 45 days, respectively. Total plant dry biomass increased by 14.71% when treated with 500 mg kg^-1 MWCNTs but decreased by 9.26% when exposed to 1000 mg kg^-1 MWCNTs. MWCNTs treatment did not affect Cd accumulation in plants. On the other hand, the bio-concentration factor of As was inversely associated with plant growth (p < 0.05), which was declined in MWCNTs treatments. Oxidative stress was aggravated when plants were exposed to MWCNTs, thus activating the antioxidant enzymes system in the corn. In contrast, TCLP-extractable Cd and As in soil significantly decreased than in the control. Additionally, the soil nutrients were changed under MWCNTs treatments. Our findings also revealed that a particular concentration of MWCNTs can mitigate the toxicity of Cd and As in corn seedlings. Therefore, these results suggest the prospective application of CNTs in agricultural production, ensuring environmental and soil sustainability.

Remediation and its biological responses to Cd(II)-Cr(VI)-Pb(II) multi-contaminated soil by supported nano zero-valent iron composites

Multi-metal contaminated soil has received extensive attention. The biochar and bentonite-supported nano zero-valent iron (nZVI) (BC-BE-nZVI) composite was synthesized in this study by the liquid-phase reduction method. Subsequently, the BC-BE-nZVI composite was applied to immobilize cadmium (Cd), chromium (Cr), and lead (Pb) in simulated contaminated soil. The simultaneous immobilization efficiencies of Cd, Cr(VI), Cr_total, and Pb were achieved at 70.95 %, 100 %, 86.21 %, and 100 %, respectively. In addition, mobility and bioavailabilities of Cd, Cr, and Pb were significantly decreased and the risk of iron toxicity was reduced. Stabilized metal species in the contaminated soil (e.g., Cd(OH)₂, Cd-Fe-(OH)₂, Cr_xFe_1-xOOH, Cr_xFe_1-x(OH)₃, PbO, PbCrO₄, and Pb(OH)₂) were formed after the BC-BE-nZVI treatment. Thus, the immobilization mechanisms of Cd, Cr, and Pb, including adsorption, reduction, co-precipitation, and complexation co-exist with the metals. More importantly, bacterial richness, bacterial diversity, soil enzyme activities (dehydrogenase, urease, and fluorescein diacetate hydrolase), and microbial activity were enhanced by applying the BC-BE-nZVI composite, thus increasing the soil metabolic function. Over all, this work applied a promising procedure for remediating multi- metal contaminated soil by using the BC-BE-nZVI composite.

Immobilization mechanism of antimony by applying zirconium-manganese oxide in soil

Antimony (Sb) accumulation in soil poses great potential risk to ecological environment, and its mobilization, transformation and bioavailability are controlled by its fractions and species. Hence, it is important to develop functional materials with both adsorption and oxidation that achieve detoxification and control the mobilization of Sb. In this study, the synthesized zirconium‑manganese oxide (ZrMn) could extremely promoted the transformation of antimonite [Sb(III)] to antimonate [Sb(V)], induced the bioavailable Sb shift to well-crystallized (hydr)oxides of Mn and residual fractions, and further reduced mobility and bioavailability Sb in soil. The sorption of ZrMn to Sb(III) and antimonate Sb(V) were affected by interfering ions, and to Sb(III) was a heterogeneous adsorption process. Spectroscopic characterization of XPS and FTIR suggested exchange between the hydroxyl groups and Sb was crucial in its retain and forming an electronegative inner-sphere mononuclear or binuclear bridging compound. The oxidation induced the transformation of Mn species in ZrMn, generated Mn(II) and Mn(III) exposing more reactive sites conducive to oxidation and adsorption, thus Mn oxides has a higher adsorption capacity for Sb(III). However, the Zr oxides of ZrMn presented adsorption rather than oxidation. The application of ZrMn could realize the dual effect of Sb oxidation detoxification and adsorption immobilization in soil, which provided references for Sb contaminated soil remediation.

Recent advances of carbon-based nano zero valent iron for heavy metals remediation in soil and water: A critical review

Heavy metal pollution in soil and water has presented a new challenge for the environmental remediation technology. Nano zero valent iron (nZVI) has excellent adsorbent properties for heavy metals, and thus, exhibits great potential in environmental remediation. Used as supporting materials for nZVI, carbon-based materials, such as activated carbon (AC), biochar (BC), carbon nanotubes (CNTs), and graphene (GNs) with aromatic rings formed by carbon atoms as the skeleton, have a large specific surface area and porous structure. This paper provides a comprehensive review on the advancement of carbon-based nano zero valent iron (C-nZVI) particles for heavy metal remediation in soil and water. First, different types of carbon-based materials and their combination with nZVI, as well as the synthesis methods and common characterization techniques of C-nZVI, are reviewed. Second, the mechanisms for the interactions between contaminants and C-nZVI, including adsorption, reduction, and oxidation reactions are detailed. Third, the environmental factors affecting the remediation efficiency, such as pH, coexisting constituents, oxygen, contact time, and temperature, are highlighted. Finally, perspectives on the challenges for utilization of C-nZVI in the actual contaminated soil and water and on the long-term efficacy and safety evaluation of C-nZVI have been proposed for further development.