Formation mechanisms and degradation methods of polycyclic aromatic hydrocarbons in biochar: A review.

Biochar has been widely used in soil amendment and environmental remediation. Polycyclic aromatic hydrocarbons (PAHs) could be produced in preparation of biochar, which may pose potential risks to the environment and human health. At present, most studies focus on the ecotoxicity potential of biochar, while there are few systematic reviews on the formation mechanisms and mitigation strategies of PAHs in biochar. Therefore, a systematical understanding of the distribution, formation mechanisms, risk assessment, and degradation approaches of PAHs in biochar is highly needed. In this paper, the distribution and content of the total and bioavailable PAHs in biochar are reviewed. Then the formation mechanisms, influencing factors, and potential risk assessment of PAHs in biochar are systematically explored. After that, the effective strategies to alleviate PAHs in biochar are summarized. Finally, suggestions and perspectives for future studies are proposed. This review provides a guide for reducing the formation of biochar-associated PAHs and their toxicity, which is beneficial for the development and large-scale safe use of environmentally friendly biochar.

Multicomponent PFAS sorption and desorption in common commercial adsorbents: Kinetics, isotherm, adsorbent dose, pH, and index ion and ionic strength effects.

The adsorption and desorption of 9 PFAS, including 3 perfluoroalkyl sulphonic and 6 perfluoroalkyl carboxylic acids, in artificial groundwater was investigated using 3 commercial adsorbents that comprised a powdered activated carbon (PAC), a surface-modified organoclay (NMC+n), and a carbonaceous organic amendment (ROAC). Sorption kinetics and isotherms of PFAS, as well as the effects of adsorbent dose, pH, index ion and ionic strength on PFAS adsorption and desorption were investigated. Sorption of multicomponent PFAS in the adsorbents was rapid, especially for NMC+n and ROAC, regardless of PFAS chain length. The sorption and (and especially) desorption of PFAS in the adsorbents was impacted by the pH, index ion, and ionic strength of simulated groundwater, especially for the short chain PFAS, with only minimal impacts on NMC+n and PAC compared to ROAC. Although the potential mineral and charged constituents of the adsorbents contributed to the adsorption of short chain PFAS through electrostatic interactions, these interactions were susceptible to variable groundwater chemistry. Hydrophobic interactions also played a major role in facilitating and increasing PFAS sorption, especially in adsorbents with aliphatic functional groups. The desorption of PFAS from the adsorbents was below 8 % when the aqueous phase was deionised water, with no measurable desorption for NMC+n. In contrast, the desorption of short chain PFAS in simulated groundwater increased substantially (30-100 %) in the adsorbents, especially in ROAC and NMC+n, but more so with ROAC. In general, the three adsorbents exhibited strong stability for the long chain PFAS, especially the perfluoroalkyl sulphonic acids, with minimal to no sorption reversibility under different pH and ionic composition of simulated groundwater. This study highlights the importance of understanding not only the sorption of PFAS in groundwater using adsorbents, but also the desorption of PFAS, which may be useful for decision making during the ex-situ and in-situ treatment of PFAS-contaminated groundwater.

Iron-modified biochar derived from sugarcane bagasse for adequate removal of aqueous imidacloprid: sorption mechanism study.

Adsorption has been considered as a promising remediation technology to separate organic and inorganic agrochemicals from contaminated soil and water. Low-cost adsorbents, including waste derived materials, clay composites, biochar, and biochar modified materials, have attracted enormous attention for the removal of organic contaminants, including pesticides. In this study, iron-modified base-activated biochar (FeBBC) was prepared by pyrolysis (at 400 °C for 1 h) of iron-doped base (KOH) activated sugarcane bagasse for the removal of a widely used insecticide, namely imidacloprid (IMI) from water. The maximum adsorption capacity of the adsorbent (FeBBC) was calculated as 10.33 (± 1.57) mg/g from Langmuir isotherm model. The adsorbents could remove up to ~ 92% of IMI from aqueous solution at 23.8 mg/L IMI. Experimental data fitted well with the Freundlich model and pseudo-second-order model, demonstrating physisorption, as well as chemosorption, contributed to the sorption process. Even at highly acidic/basic solution pH, the FeBBC could remove substantial amount of IMI demonstrating hydrophobic interaction and pore diffusion play vital role for removal of IMI. The slight improving of IMI sorption with increasing solution pH indicated the sorption was also facilitated through ionic interaction alongside physical sorption. However, physical sorption including hydrophobic interaction and pore-filling interaction plays a vital role in the sorption of IMI.

Detection of Leptin Using Electrocatalyst Mediated Impedimetric Sensing.

Obesity is a complex disorder associated with immense health consequences including high risk of cardiovascular diseases, diabetes, and cancer. Abnormality in the thyroid gland, genetics, less physical activity, uptake of excessive diet, and leptin resistance are critical factors in the development of obesity. To determine the treatment strategy, understanding the pathophysiology of obesity is crucial. For instances, leptin resistance mediated obesity defined by the presence of excessive leptin hormone (Lep) in the systemic circulation is very common in diet induced obesity. Therefore, our hypothesis is that quantitative measurement of Lep from blood can help to identify individuals with Lep resistant mediated obesity and thereby guide toward a proper treatment strategy. In this work, we aim to utilize an electrochemical immunosensing platform for diagnosis of obesity by measuring the Lep content in systemic circulation. A porous carbon confined FeNi bimetallic system was synthesized with three different ratios of Fe and Ni ions using high temperature pyrolysis technique. The suitability of the sensor for detecting Lep was studied using both CV and EIS techniques. The limit of detection (LOD) for GCE was recorded as 157.4 fg/mL with a wide linear concentration range of 500 fg/mL to 80 ng/mL, while for SPCE the LOD was 184.9 fg/mL with a linear range of 500 fg/mL to 50 ng/mL. Finally, the feasibility and applicability of the sensor for Lep detection was tested with serum collected from high fat diet induced obese rats. The selectivity, sensitivity, storage, and experimental stability and reproducibility tests showed potential for this biosensor platform as a point-of-care Lep detection device.

Magnetic responsive mesoporous alginate/ß-cyclodextrin polymer beads enhance selectivity and adsorption of heavy metal ions.

Mesoporous (~7-8 nm) biopolymer hydrogel beads (HNTs-FeNPs@Alg/ß-CD) were synthesised via ionic polymerisation route to separate heavy metal ions. The adsorption capacity of HNTs-FeNPs@Alg/ß-CD was higher than that of raw halloysite nano tubes (HNTs), iron nanoparticles (FeNPs), and bare alginate beads. FeNPs induce the magnetic properties of adsorbent and metal-based functional groups in and around the hydrogel beads. The mesoporous surface of the adsorbent permits access of heavy metal ions onto the polymer beads to interact with internal active sites and the mesoporous polymer network. Maximum adsorption capacities of lead (Pb), copper (Cu), cadmium (Cd), and nickel (Ni) were 21.09 mg/g, 15.54 mg/g, 2.47 mg/g, and 2.68 mg/g, respectively. HNTs-FeNPs@Alg/ß-CD was able to adsorb heavy metals efficiently (75-99%) under environment-relevant concentrations (200 µg/L) from mixed metal contaminants. The adsorption and selectivity trends of heavy metals were Pb > Cu > Cd > Ni, despite electrostatic binding strength of Cd > Cu > Pb > Ni and covalent binding strength of Pb > Ni > Cu > Cd. It demonstrated that not only chemosorption but also physisorption acts as the sorption mechanism. The reduction in surface area, porosity, and pore volume of the expended adsorbent, along with sorption study results, confirmed that pore filling and intra-particle diffusion played a considerable role in removing heavy metals.

Mesoporous Biopolymer Architecture Enhanced the Adsorption and Selectivity of Aqueous Heavy-Metal Ions.

Halloysite nanotubes (HNT) and ball-milled biochar (BC) incorporated biocompatible mesoporous adsorbents (HNT-BC@Alg) were synthesized for adsorption of aqueous heavy-metal ions. HNT-BC@Alg outperformed the BC, HNT, and BC@Alg in removing cadmium (Cd), copper (Cu), nickel (Ni), and lead (Pb). Mesoporous structure (∼7.19 to 7.56 nm) of HNT-BC@Alg was developed containing an abundance of functional groups induced from encapsulated BC and tubular HNT, which allowed heavy metals to infiltrate and interact with the adsorbents. Siloxane groups from HNT, oxygen-containing functional groups from BC, and hydroxyl and carboxyl groups from alginate polymer play a significant role in the adsorption of heavy-metal ions. The removal percentage of heavy metals was recorded as Pb (∼99.97 to 99.05%) > Cu (∼95.01 to 90.53%) > Cd (∼92.5 to 55.25%) > Ni (∼80.85 to 50.6%), even in the presence of 0.01/0.001 M of CaCl2 and Na2SO4 as background electrolytes and charged organic molecule under an environmentally relevant concentration (200 µg/L). The maximum adsorption capacities of Ni, Cd, Cu, and Pb were calculated as 2.85 ± 0.08, 6.96 ± 0.31, 16.87 ± 1.50, and 26.49 ± 2.04 mg/g, respectively. HNT-BC@Alg has fast sorption kinetics and maximum adsorption capacity within a short contact time (∼2 h). Energy-dispersive X-ray spectroscopy (EDS) elemental mapping exhibited that adsorbed heavy metals co-distributed with Ca, Si, and Al. The reduction of surface area, pore volume, and pore area of HNT-BC@Alg (after sorption of heavy metals) confirms that mesoporous surface (2-18 nm) supports diffusion, infiltration, and interaction. However, a lower range of mesoporous diameter of the adsorbent is more suitable for the adsorption of heavy-metal ions. The adsorption isotherm and kinetics fitted well with the Langmuir isotherm and the pseudo-second-order kinetic models, demonstrating the monolayer formation of heavy-metal ions through both the physical sorption and chemical sorption, including pore filling, ion exchange, and electrostatic interaction.

Influences of feedstock sources and pyrolysis temperature on the properties of biochar and functionality as adsorbents: A meta-analysis.

Biochar is a porous, amorphous, stable, and low-density carbon material derived from the carbonization of various biological residues. Biochars have multifunctional properties that make them promising adsorbents for the remediation of organic and inorganic contaminants from soil and water. High temperature treatment (HTT) and the properties of feedstocks are key factors influencing the properties of biochars. Feedstocks have distinctive physicochemical properties due to variations in elemental and structural composition, and they respond heterogeneously to specific pyrolysis conditions. The criteria for the selection of feedstocks and pyrolysis conditions for designing biochars for specific sorption properties are inadequately understood. We evaluated the influence of pyrolysis temperature on a wide range of feedstocks to investigate their effects on biochar properties. With increasing HTT, biochar pH, surface area, pore size, ash content, hydrophobicity and O/C vs. H/C (ratios that denote stability) increased, whereas, hydrophilicity, yield of biochar, O/C, and H/C decreased. Discriminant analysis of data from 533 published datasets revealed that biochar derived from hardwood (HBC) and softwood generally have greater surface area and carbon content, but lower content of oxygen and mineral constituents, than manure- (MBC) and grass-derived biochars (GBC). GBC and MBC have abundant oxygen-containing functional groups than SBC and HBC. The sequence of stability and aromaticity of feedstocks was MBC < GBC < SBC < HBC. Therefore, SBC and HBC are suitable for sorption of hydrophobic molecules. Biochars produced from low HTT are suitable for removal of ionic contaminants, whereas those produced at high HTT are suitable for removal of organic contaminants. The influences of biochar properties on sorption performance of heavy metals and organic contaminants are critically reviewed.

Critical review of magnetic biosorbents: Their preparation, application, and regeneration for wastewater treatment.

The utilisation of magnetic biosorbents (metal or metal nanoparticles impregnated onto biosorbents) has attracted increasing research attention due to their manipulable active sites, specific surface area, pore volume, pore size distribution, easy separation, and reusability that are suitable for remediation of heavy metal(loid)s and organic contaminants. The properties of magnetic biosorbents (MB) depend on the raw biomass, properties of metal nanoparticles, modification/synthesis methods, and process parameters which influence the performance of removal efficiency of organic and inorganic contaminants. There is a lack of information regarding the development of tailored materials for particular contaminants and the influence of specific characteristics. This review focuses on the synthesis/modification methods, application, and recycling of magnetic biosorbents. In particular, the mechanisms and the effect of sorbents properties on the adsorption capacity. Ion exchanges, electrostatic interaction, precipitation, and complexation are the dominant sorption mechanisms for ionic contaminants whereas hydrophobic interaction, interparticle diffusion, partition, and hydrogen bonding are the dominant adsorption mechanisms for removal of organic contaminants by magnetic biosorbents. In generally, low pyrolysis temperatures are suitable for ionic contaminants separation, whereas high pyrolysis temperatures are suitable for organic contaminants removal. Additionally, magnetic properties of the biosorbents are positively correlated with the pyrolysis temperatures. Metal-based functional groups of MB can contribute to an ion exchange reaction which influences the adsorption capacity of ionic contaminants and catalytic degradation of non-persistent organic contaminants. Metal modified biosorbents can enhance adsorption capacity of anionic contaminants significantly as metal nanoparticles are not occupying positively charged active sites of the biosorbents. Magnetic biosorbents are promising adsorbents in comparison with other adsorbents including commercially available activated carbon, and thermally and chemically modified biochar in terms of their removal capacity, rapid and easy magnetic separation which allow multiple reuse to minimize remediation cost of organic and inorganic contaminants from wastewater.

Holistic approach to pre-operative assessment for cataract patients.

When patients agree to have cataract surgery it is important that they are fully assessed to determine their fitness for surgery. This article discusses the benefits of a nurse-led holistic approach to patient assessment, which, in practice, should be more than simply a 'tick-box exercise'. Essential components of the assessment include obtaining valid informed consent and performing biometry - the process by which the required dioptric power of an intraocular lens (IOL) implant is calculated prior to cataract surgery. It is a highly skilled procedure, which involves the measurement of corneal curvature and the axial length of the eye using either ultrasound or optical methods of biometry. This article examines the vital nursing roles aimed at improving the quality and efficiency of the patient's 'journey'.