Surface activated carbon nanospheres for fast adsorption of silver ions from aqueous solutions

Development of the Pipette-Tip Micro-Solid-Phase Extraction for Extraction of Rutin From Moringa oleifera Lam. Using Activated Hollow Carbon Nanospheres as Sorbents

Herein, a micro-solid-phase extraction (μSPE) method was developed using a pipette tip for rutin extraction, employing activated hollow carbon nanospheres (HCNSs) as the sorbent. Characterization of the activated carbon nanospheres through TGA, FTIR, and SEM analysis confirmed the success of the activation process. The study demonstrated the efficacy of PT-μSPE in rutin extraction under pH 2 conditions with a standard concentration of 2 mg·L-1. The optimal mass of HCNSs was found to be 2 mg, and a loading volume of 500 μL resulted in the maximum recovery of rutin. Propan-2-ol was the best elution solvent with 15 aspirating/dispensing cycles. The correlation of determination (R 2) for the calibration curve was found to be 0.9991, and the LOD and LOQ values were 0.604 and 1.830 mg·L-1, respectively. The applicability of the method was demonstrated by extracting rutin from a complex Moringa oleifera leaf extract with the relative standard deviation (RSD) of 3.26%, thereby validating this method as feasible for the extraction of useful bioactive compounds from complex plant samples.

Carbon Dioxide Adsorption over Activated Biocarbons Derived from Lemon Peel

The rising concentration of CO2 in the atmosphere is approaching critical levels, posing a significant threat to life on Earth. Porous carbons derived from biobased materials, particularly waste byproducts, offer a viable solution for selective CO2 adsorption from large-scale industrial sources, potentially mitigating atmospheric CO2 emissions. In this study, we developed highly porous carbons from lemon peel waste through a two-step process, consisting of temperature pretreatment (500 °C) followed by chemical activation by KOH at 850 °C. The largest specific surface area (2821 m2/g), total pore volume (1.39 cm3/g), and micropore volume (0.70 cm3/g) were obtained at the highest KOH-to-carbon ratio of 4. In contrast, the sample activated with a KOH-to-carbon ratio of 2 demonstrated the greatest micropore distribution. This activated biocarbon exhibited superior CO2 adsorption capacity, reaching 5.69 mmol/g at 0 °C and 100 kPa. The remarkable adsorption performance can be attributed to the significant volume of micropores with diameters smaller than 0.859 nm. The Radke-Prausnitz equation, traditionally employed to model the adsorption equilibrium of organic compounds from liquid solutions, has been shown to be equally applicable for describing the gas-solid adsorption equilibrium. Furthermore, equations describing the temperature dependence of the Radke-Prausnitz equation's parameters have been developed.

Regulating the Interface Polarity Distribution of Zr-Based MOFs by Amino Acid-Like Ligand Functionalization Enables Efficient Recovery of Gold

The recovery of gold from industrial effluents is crucial for environmental conservation, sustainable resource management, and promoting the green development of gold resources. We designed a Zr-based MOF (UKM-78) by incorporating functional organic ligands that resemble amino groups, using MOFs' inherent sieving effect for ion separation. This novel material exhibited enhanced gold recovery under acidic conditions, with an adsorption capacity three times and an adsorption rate four times higher than those of nonfunctionalized UKM-77. Notably, UKM-78 efficiently captured gold solutions at concentrations as low as 1 ppm and achieved an adsorption rate exceeding 90%, owing to the electrostatic interactions and coordination between its functionalized groups and the synergistic effect of its porous structure. Despite multiple regeneration cycles, UKM-78 retains 99.4% of its adsorption capacity. X-ray photoelectron spectroscopy (XPS), kinetic studies, and thermodynamics collectively demonstrated that Au(III) binding on UKM-78 involved cooperative electrostatic interactions and chemical adsorption through coordination. This study highlights the potential of MOFs for efficient and sustainable recovery of gold from complex waste streams.

A zirconium metal-organic framework functionalized with a S/N containing carboxylic acid (MOF-808(Zr)-Tz) as an efficient sorbent for the ultrafast and selective dispersive solid phase micro extraction of chromium, silver, and rhodium in water samples

Metal-organic frameworks (MOFs) are good adsorbents for targeted chemicals with their adjustable properties. Herein, we prepared a zirconium based MOF (MOF-808(Zr)) and functionalized it employing 2-mercapto-4-methyl-5-thiazolacetic acid (MOF-808(Zr)-Tz). The prepared MOFs were characterized by XRD, FTIR, SEM-EDX, TGA, N2 sorption, zeta potential measurements, and elemental analysis. The surface area of MOF-808(Zr)-Tz was 1348 m2/g. Dispersive solid-phase micro-extraction (D-SPµE) method based on MOF-808(Zr)-Tz was firstly developed and applied to the extraction of chromium, silver, and rhodium in waters. The determination of the analytes was done by FAAS. The optimal pH and eluent for analytes were 7.0 and 3 mL of 2 mol L-1 HCl, respectively. The contact times were 1 min for adsorption and 3 min for elution. The LOD and PFs of the D-SPμE for analytes were 2.3 μg L-1 and 13.3 for chromium, 2.1 μg L-1 and 13.3 for silver, and 3.1 μg L-1 and 13.3 rhodium, respectively. The D-SPμE method was verified with analyses of NW-TMDA-54.6 Lake water and SPS-WW1 Batch 114 Wastewater and with spiked dam water, river water, well water, sea water, and wastewater. The recoveries of the analytes changed from 89 to 108 %. The results indicated that the method is selective, simple, effective, and rapid for extracting chromium(III), silver(I) and rhodium(III) in waters.

Synthesis of metal-organic frameworks with multiple nitrogen groups for selective capturing Ag(I) from wastewater

As a noble metal with extremely high economic benefits, the recovery of silver ions has attracted a particular deal of attention. However, it is a challenge to recover silver ions efficiently and selectively from aqueous solutions. In this research, the novel metal-organic frameworks (MOFs) adsorbent (Zr-DPHT) is prepared for the highly efficient and selective recovery of silver ions from wastewater. Experimental findings reveal that Zr-DPHT's adsorption of Ag(I) constitutes an endothermic process, with an optimal pH of 5 and exhibits a maximum adsorption capacity of 268.3 mg·g-1. Isotherm studies show that the adsorption of Ag(I) by Zr-DPHT is mainly monolayer chemical adsorption. Kinetic studies indicate that the internal diffusion of Ag(I) in Zr-DPHT may be the rate-limiting step. The mechanism for Ag(I) adsorption on Zr-DPHT involves electrostatic interactions and chelation. In competitive adsorption, Ag(I) has the largest partition coefficient (9.64 mL·mg-1), indicating a strong interaction between Zr-DPHT and Ag(I). It is proven in the adsorption-desorption cycle experiments that Zr-DPHT has good regeneration performance. The research results indicate that Zr-DPHT can serve as a potential adsorbent for efficiently and selectively capturing Ag(I), providing a new direction for MOFs in the recycling field of precious metals.

Preparation of activated carbon from sewage sludge using green activator and its performance on dye wastewater treatment

The remediation of dyes in wastewater using activated carbon produced from sewage sludge pyrolysis char (PYC) is an environmentally friendly and sustainable process. However, traditional activators can cause corrosion of the processing facility, thereby increasing the costs of waste disposal. Here, activated carbons were prepared from sewage sludge PYC, and the effects of activation conditions (different activators, temperature and time, and char:activator mass ratio) on their specific surface areas and adsorption of iodine and methylene blue (MB; model dye) were studied. The results showed that a value of 952 m2/g could be attained for the specific surface area and values of 882 and 162 mg/g for the adsorption of iodine and MB, respectively, by heating PYC with KHCO3 (PYC- KHCO3: 1:2 w/w) for 60 min at 800 ℃. Compared with activation by KOH, the adsorption of MB using PYC-KHCO3 was slightly lower but the yield was 13.7% higher. Optimization of the activation process using surface response modelling indicated that sensitivity of three key factors to the adsorption of iodine and MB followed the order: Mass ratio > temperature > time. Systematic investigation of the effects of time, pH and temperature on the removal of MB by the activated carbon revealed that adsorption conformed to the Langmuir model and pseudo-second-order kinetics. The proposed mechanisms of MB adsorption involved ion exchange, functional group complexation and physical/π-π interactions. This study provides a basis for the efficient remediation of dyes in wastewater using activated carbon prepared from sustainable sewage sludge PYC and green chemistry.

An effective uranium removal using diversified synthesized cross-linked chitosan bis-aldehyde Schiff base derivatives from aqueous solutions

Three new cross-linked chitosan derivatives were yielded through intensification of chitosan with diverse types of bis-aldehydes. The prepared cross-linked chitosan was characterized by FTIR, 1H NMR, XRD, and TGA techniques. TGA indicated an improvement in thermal stability of the cross-linked chitosan compared with pure chitosan. Batch adsorption experiments showed that the three novel cross-linked chitosan bis-aldehyde derivatives possessed good adsorption capacity against U(VI) in the order of BFPA > BFB > BODB (adsorption capacity of the three adsorbents for U(VI) reaches 142, 124, and 114 mg/g respectively) and the adsorption isotherm and kinetic were well described by the Langmuir and the pseudo-second-order kinetic model, respectively. In addition, the prepared cross-linked chitosan bis-aldehyde derivatives were examined as U(VI) catcher from waste solutions.

Silver nanoparticles deposited carbon microspheres nanozyme with enhanced peroxidase-like catalysis for colorimetric detection of Hg2+ in seafood

Novel methods for high-performance detection of Hg²⁺ in seafood are critical for ensuring food safety and human health. Herein, Ag nanoparticles (Ag NPs) were successfully deposited on carbon microspheres (CMs) to form Ag NPs-CMs nanocomplex. The proposed Ag NPs-CMs could oxidize colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidation state TMB (oxTMB) in the presence of hydrogen peroxide (H₂O₂) and had a significant UV-vis absorption peak at 652 nm. The excellent peroxidase-like activity was attributed to the increased electrostatic attraction of CMs and the catalytic synergistic effect. After adding Hg²⁺, the catalytic activity of Ag NPs-CMs was specifically enhanced and the Michaelis-Menten constant (K_m) decreased from 0.067 to 0.052 mmol/L due to the formation of Ag-Hg amalgam which produced more superoxide anions (O₂^•-) and hydroxyl radicals (•OH). The linear response ranges for Hg²⁺ were 2~833 nmol/L and 2.5~40 μmol/L, with the low detection limit of 1.10 nmol/L. This method was applied to detect Hg²⁺ in seafood with satisfactory recoveries of 95.65~106.56%. A hydrogel kit was designed for portable detection of Hg²⁺, and the response range was 0.5~5 μmol/L. This work provides a reliable method for visual Hg²⁺ detection in seafood as well as a feasible strategy for the design of high-performance nanozymes.

Functionalized agarose hydrogel with in situ Ag nanoparticles as highly recyclable heterogeneous catalyst for aromatic organic pollutants

In the present research work, a highly recyclable catalyst of Ag-based agarose (HRC-Ag/Agar) hydrogel was successfully fabricated through a simple and efficient in situ reduction method without the aid of additional surface active agent. The interaction between the rich hydroxyl functional (-OH) groups in agarose and Ag can effectively control the growth and dispersion of Ag nanoparticles (NPs) in the HRC-Ag/Agar hydrogel and keep Ag NPs free from chemical contamination, which also guarantees the reusability of HRC-Ag/Agar hydrogel as catalysts. HRC-Ag/Agar hydrogel without freeze drying and calcination was investigated for their potential applications as highly active/recyclable catalysts in reducing aromatic organic pollutants (p-nitrophenol (4-NP), methylene blue (MB) and rhodamine B (RhB)) by KBH₄. The optimal HRC-Ag/Agar-1.9 hydrogel can complete the catalytic reduction of 4-NP within 11 min. Moreover, HRC-Ag/Agar-1.9 hydrogel achieves the high conversion rate (> 99%) through ten catalytic runs. Similarly, HRC-Ag/Agar-1.9 hydrogel was able to achieve a reduction efficiency of RhB at 98% within 17 min and that of MB at 95% within 40 min. The advantages of simple synthetic procedure, no secondary pollution, strong stability and easily separated make the HRC-Ag/Agar hydrogel have great potential prospect for environmental applications.

Biomass-Based Hydrothermal Carbons for the Contaminants Removal of Wastewater: A Mini-Review

The preparation of adsorbents with eco-friendly and high-efficiency characteristics is an important approach for pollutant removal, and can relieve the pressure of water shortage and environmental pollution. In recent studies, much attention has been paid to the potential of hydrothermal carbonization (HTC) from biomass, such as cellulose, hemicellulose, lignin, and agricultural waste for the preparation of adsorbents. Hereby, this paper summarizes the state of research on carbon adsorbents developed from various sources with HTC. The reaction mechanism of HTC, the different products, the modification of hydrochar to obtain activated carbon, and the treatment of heavy metal pollution and organic dyes from wastewater are reviewed. The maximum adsorption capacity of carbon from different biomass sources was also evaluated.

Single-walled carbon nanotube gutter layer supported ultrathin zwitterionic microporous polymer membrane for high-performance lithium-sulfur battery

Development of efficient lithium-sulfur (Li-S) battery requires the need to develop an appropriate functional separator that allows strong facilitation and transport of lithium ions together with limited passage of polysulfides. In this work, a multifunctional separator (TB-BAA/SWCNT/PP) is developed through spin coating of a novel zwitterionic microporous polymer (TB-BAA) on the gutter layer constructed from single-walled carbon nanotubes (SWCNT), where commercially available polypropylene (PP) separator is used to act as the mechanical support. SWCNT in this study serves as the first modification layer to decrease the size of the macropores in the PP separator, while the ultrathin TB-BAA top barrier layer with the presence of zwitterionic side chains allows the creation of confined ionic channels with both lithiophilic and sulfophilic groups. Due to the presence of available chemical interactions with lithium polysulfides, selective ion transport can be foreseen through such separator. In this regard, shuttle effect that is frequently encountered in Li-S battery can be suppressed effectively via implementing the as-obtained functional separator, resulting in the creation of credible and stable sulfur electrochemistry. The TB-BAA/SWCNT/PP-based Li-S battery has been investigated to possess high cycling ability (capacity fading per cycle of 0.055% over 500 cycles at 1 C) together with decent rate capability (736.6 mAh g^-1 at 3 C). In addition, a high areal capacity retention of 5.03 mAh cm^-2 after 50 cycles can be also obtained under raised sulfur loading (5.4 mg cm^-2).

Impact of sulfhydryl ligands on the transformation of silver ions by molybdenum disulfide and their combined toxicity to freshwater algae

The transformation of silver ions (Ag⁺) mediated by engineered nanomaterials (ENMs) influences the biosafety of Ag-containing products in natural environments. Actually, modification of biomolecules to ENMs in aquatic ecosystems alters their interactions with Ag⁺. This study discovered that surface functionalization of glutathione (GSH, a sulfhydryl compound ubiquitous in natural waters) on molybdenum disulfide (MoS₂) nanoflakes suppressed the redox reaction between 1 T components and Ag⁺, inhibiting the MoS₂-mediated reduction of Ag⁺ to Ag nanoparticles (AgNPs) in aqueous phase in the dark. However, AgNPs formation (from 2.32 ± 0.35-3.25 ± 0.29 mg/L per day, pH 7.0) and oxidation of MoS₂ were remarkably accelerated after GSH binding under light conditions. The dominant electron donator of MoS₂ to Ag⁺ was transformed from the electron-hole pairs to surface ligands driven by the introduction of chromophoric groups was authenticated as the cause for the elevated Ag⁺ reduction. These processes also occurred between Ag⁺ and MoS₂ at low levels (50 μg/L). Additionally, the joint algal toxicity of GSH-modified MoS₂ with Ag⁺ was weaker than that of pristine MoS₂ due to increased retention of free Ag⁺ and AgNPs formation. Our findings improve the understanding of the interaction between ENMs and Ag⁺ in aquatic ecosystems.

Recent advances of carbon-based nanomaterials (CBNMs) for wastewater treatment: Synthesis and application

Carbon-based nanomaterials (CBNMs) have attracted significant alert due to the affluent science underpinning their implementations associated with a novel mixture of high aspect proportions, greater thermal and electrical performance, outstanding optical features, and high exterior area. CBNMs not only bear assurance in a broad range of implementations in medication, nano and microelectronics, and ecological remedies but may also be utilized in practical laboratory determinations. More specifically, CBNMs perform as an outstanding adsorbent in terminating heavy metal ions (HMI) from wastewater. There is presently a deficiency of powerful threat inspection instruments owing to their complex detection and related deficit in the health risk database. Therefore, our present review concentrates on spreading CBNMs to release pollutants from wastewater. The article wraps the effect of these contaminants and photocatalytic strategies towards treating these mixtures in wastewater, along with their restrictions and challenges, convincing resolutions, and possibilities of these approaches.

Volcanic rock powder residues as precursors for the synthesis of adsorbents and potential application in the removal of dyes and metals from water

The present study verified the potential of volcanic rock powder residues originating from the extraction of semi-precious rocks in the state of Rio Grande do Sul, Brazil, as precursors or adsorbents for dyes and metallic ion removal from water. In this way, it is possible to add value and give an adequate destination to this waste. Volcanic rock powder residues from Ametista do Sul (AME) and Nova Prata (NP) were the starting materials. These were used naturally or submitted to the alkaline activation process at 60 °C and alkaline fusion at 550 °C. The analysis of the starting samples by X-ray fluorescence (XRF) revealed that they are mainly composed of aluminum, calcium, iron, and silicon oxides, which corroborates the presence of numerous crystalline phases observed in the X-ray diffraction spectra (XRD). Moreover, by XRD analysis of the synthesized samples, alkaline fusion proved to be more efficient in the dissolution of crystalline phases and consequently in the formation of the amorphous phase (more reactive). Furthermore, the adsorption tests with acid green and acid red dyes and Ag⁺, Co²⁺, and Cu²⁺ ions indicated the viability of using residual volcanic rock powder as raw material for the production of adsorbents functionalized with sodium hydroxide, being that the samples synthesized by alkaline fusion showed better results of removal and adsorption capacity for all the contaminants used in the study.

Efficient and selective removal of Ag+ as nano silver particles by the composite of SiO2 supported nano ferrous oxalate

Developing novel environmentally materials with high capacity and selectivity for Ag⁺ adsorption by transforming Ag⁺ to nano silver is important for the recovery of precious metals from Ag-containing solution. The present study systematically studied the Ag ⁺ adsorption process from solution by the composite of SiO₂ supported nano ferrous oxalate (SNFO) synthesized from biotite-containing minerals. Batch experiments, dynamics and isothermal adsorption fitting results showed that Ag⁺ removal behaviours were in accordance with the pseudo-first-order kinetic model and Langmuir model, and the maximal Ag⁺ removal capacity was 223.68 mg/g. Thermodynamic fitting results suggested that Ag ⁺ removal by the composite was a spontaneous and endothermic reaction process. XRD and TEM revealed that the reaction products were consisted of SiO₂ and nano silver particles, and FTIR and XPS results indicated that the Ag⁺ removal mechanisms were attributed to the synergistic reduction interaction between ferrous and the anions of oxalate. Meanwhile, the composite possesses high selectivity for Ag⁺ removal even at low Ag⁺ concentration. Moreover, the size of nano silver particles could be adjusted by different pH values. All above results demonstrated that the composite was an ideal material for selective recovery of Ag⁺ from Ag⁺ containing effluents in the form of nano silver.

Recovery of Copper(II) and Silver(I) from Nitrate Leaching Solution of Industrial Dust via Solvent Extraction with LIX63

A nitrate leachate containing Cu(II), Ag(I), Ni(II), Mg(II), and Al(III) was obtained during the leaching of industrial dust, which arises during the pyrometallurgy of spent camera modules. To separate and recover Cu(II) and Ag(I) from the leaching solution, solvent extraction experiments using 5,8-diethyl-7-hydroxydodecan-6-oxime (LIX63) were conducted. LIX63 was found to selectively extract Cu(II) and Ag(I) over other metal ions (Ni(II), Mg(II), and Al(III)) at low nitric acid concentrations. The extraction efficiency of Cu(II) was more affected than that of Ag(I) by the acidity of the feed solution and the LIX63 concentration in the organic phase. Cu(II) and Ag(I) were simultaneously extracted using 2 mol/L LIX63. Cu(II) was separated from the loaded LIX63 via stripping with 4 mol/L HNO3, whereas Ag(I) was recovered via stripping with 0.1 mol/L thiourea after the removal of Cu(II). McCabe–Thiele diagrams for the extraction and stripping of Cu(II) and Ag(I) were constructed. The complete extraction of Cu(II) and Ag(I) was confirmed via counter-current extraction. Moreover, stripping simulation tests confirmed that higher than 99.99% of Cu(II) and 99.2% of Ag(I) were stripped. The purities of Cu(II) and Ag(I) in the recovered solution were 95.2% and 99.993%, respectively. A process flow chart for the recovery of Cu(II) and Ag(I) from the nitrate leachate of the target industrial dust was also provided.

Photoinduced transformation of silver ion by molybdenum disulfide nanoflakes at environmentally relevant concentrations attenuates its toxicity to freshwater algae

The transformation of Ag⁺ is strongly correlated with its risks in aquatic environment. Considering the wide application of molybdenum disulfide (MoS₂) and the inevitable release into the environment, the effects of MoS₂ on Ag⁺ transformation and toxicity are of great concerns. This study revealed the pH-dependent reduction of Ag⁺ (0.5 mM) to Ag nanoparticles (AgNPs) by MoS₂ (50 mg/L) and solar irradiation obviously accelerates the AgNPs formation (2.638 mg/L per day, pH=7.0) compared with dark condition (0.637 mg/L per day), ascribing to the electrons capture from electron-hole pairs of MoS₂ by Ag⁺. Ionic strengths and natural organic matter decreased the AgNPs yield. Metallic 1 T phase of MoS₂ primarily participated in AgNPs formation and was oxidized to soluble ions (MoO₄^2-) due to the oxygen generation in valance band. The above processes also occurred between Ag⁺ and MoS₂ at environmentally relevant concentrations. Further, photoinduced transformation of Ag⁺ by MoS₂ (10-100 μg/L) significantly lowered its toxicity to freshwater algae. The AgNPs formation on MoS₂ reduced the bioavailability of Ag⁺ to algae, which was the mechanism for attenuated Ag⁺ toxicity. The provided data are helpful for better understanding the roles of MoS₂ on the environmental fates and risks of metal ions under natural conditions.

A critical review on silver nanoparticles: From synthesis and applications to its mitigation through low-cost adsorption by biochar

Silver nanoparticles are one of the most beneficial forms of heavy metals in nanotechnology applications. Due to its exceptional antimicrobial properties, low electrical and thermal resistance, and surface plasmon resonance, silver nanoparticles are used in a wide variety of products, including consumer goods, healthcare, catalysts, electronics, and analytical equipment. As the production and applications of silver nanoparticles containing products increase daily, the environmental pollution due to silver nanoparticles release is increasing and affecting especially the aqueous ecosystem. Silver nanoparticles can kill useful bacteria in soil and water, and bioaccumulate in living organisms even at low concentrations from 10^-2 to 10 μg/mL silver can show antibacterial effect. On the other hand, the maximum silver discharge limit into freshwater is 0.1 μg/L and 3.2 μg/L for Australia and the USA, respectively. To reduce its toxic consequences and meet the regulatory guidelines, it is crucial to remove silver nanoparticles from wastewater before it is discharged into other water streams. Several technologies are available to remove silver nanoparticles, but the adsorption process using low-cost adsorbents is a promising alternative to mitigate silver nanoparticle pollution in the bulk stage. As one of the low-cost adsorbents, biochar produced from the biomass waste could be a suitable adsorbent. This review focuses on collating the latest evidence on silver nanoparticle production, applications, environmental consequences, and cost-effective technological approaches for silver removal from wastewater.

Bacterially self-assembled encapsulin nanocompartment for removing silver from water

Compartmentalization can protect cells from the interference of external toxic substances by sequestering toxic products. We hypothesized that proteinaceous nanocompartments may be a feasible candidate material to be added to genetically modified bacteria for the sequestration of toxic environmental products, which would open up a new bioremediation pathway. Here, we showed that the model bacterium (Escherichia coli) with self-assembling nanocompartments can remove silver (Ag) from water. Transmission electron microscopy and energy dispersive X-ray (TEM-EDX) analysis showed that the nanocompartments combined stably with silver in vitro. In addition, when exposed to 30 μM AgNO₃, the survival rate of genetically modified bacteria (with nanocompartments) was 86%, while it was just 59% in the wild-type bacteria (without nanocompartments). Label-free quantitative proteomics indicated that the nanocompartments enhanced bacterial activity by inducing the up-regulation of protein processing and secondary metabolites, and decreased their intracellular silver concentration, both of which contributed to their increased resistance to toxic silver. This study on nanocompartments has contributed to a deeper understanding of how bacteria respond to environmental stressors like heavy metal pollutants in water. The technology promises to provide a new strategy for recycling heavy metals from sewage.

Simple in situ functionalization of carbon nanospheres

Functionalized carbon nanospheres have been synthesized in situ via a facile chemical vapor deposition strategy, fabricated by the pyrolysis of toluene/ethanol mixtures at different percentages (0, 1, 2, 3, 4, and 5 wt% of ethanol). The as-grown nanospheres have been characterized using transmission electron microscopy, scanning electron microscopy, Raman and Fourier transform infrared spectroscopy, x-ray diffraction, nitrogen adsorption, zeta potential measurements and x-ray photoelectron spectroscopy. Results indicate that the incorporation of ethanol in the precursor solution reflected in the presence of oxygen and hydrogen functional groups, the highest functionalized nanospheres without compromising the morphology of the sample were yielded at 3 wt% concentration. These in situ added functional groups rendered the carbon nanostructures enhancedly dispersible and stable in water, avoiding post-synthesis and harsh chemicals processing; envisaging thus applications of the nanospheres in the biomedical field where hydrophilicity of the nanomaterials is mandatory.

Fast and effective recovery of Au(III) from aqueous solution by a N-containing polymer

In this work, a N-containing polymer was successfully synthesized by one-step treatment with 3-amine-1,2,4-triazole ligands and Zn(II) using the thermal solvent method, and employed to recover Au(III) from water. The adsorption kinetics was comprehensively studied through kinetics models including pseudo-first-order model, pseudo-second-order model, moving boundary model and Weber-Morris model. It is found that the overall adsorption rate was determined by chemical adsorption, and the rate-limiting step of diffusion steps is film diffusion. Rising temperature can improve the adsorption rate significantly, making the adsorption equilibrium time be reduced from 6 h at 298 K to 2 h at 318 K. The adsorption isotherm can be described well by Sips model, indicating it is a heterogeneous adsorption. The material shows high adsorption capacity towards Au(III) up to 1073 mg/g. It shows strong affinity towards Au(III) in the mixture solutions containing Au(III), Cu(II), Zn(II), Co(II), Cd(II), Pb(II) and Ni(II) ions. The material can be easily and completely desorbed by thiourea solution and still maintains its adsorption performance only with a slight decrease after three cycles. Combined with studies on pH influence, adsorption kinetics, adsorption isotherm and XPS analysis, it can be concluded that the adsorption mechanism could be attributed to electrostatic interaction, the coordination of the Zn-OH and -C-N/-CN- with Au(III), and partial reduction of Au(III) to Au(I) by -NH group on the polymer. The N-containing polymer is an excellent candidate for Au(III) recovery efficiently and selectively from aqueous solution.

Review on sustainable production of biochar through hydrothermal liquefaction: Physico-chemical properties and applications

This review examines in detail the production and characteristics of biochar resulting from hydrothermal liquefaction. Specifically, the impact of feedstocks and different process parameters on the properties and yield of biochar by hydrothermal liquefaction has been thoroughly studied. Hydrothermal liquefaction derived biochars, relative to biochars from high-temperature thermochemical processes retain critical functional groups during carbonization and are therefore promising for a wide range of applications. Most of the review's efforts are to study possible hydrothermal liquefaction biochar applications in various fields, including fuel, metal and dye adsorption, pollutant reduction, animal feed, and biogas catalyst. The feasibility of biochar through the hydrothermal liquefaction process has been analysed via life-cycle assessment and energy evaluation. The article concludes with a brief discussion on possible issues and strategies for the sustainable development of hydrothermal liquefaction-based biochar.

Green Synthesis of S- and N-Codoped Carbon Nanospheres and Application as Adsorbent of Pb (II) from Aqueous Solution

In this paper, green and facile synthesis of sulfur- and nitrogen-codoped carbon nanospheres (CNs) was prepared from the extract of Hibiscus sabdariffa L by a direct hydrothermal method. Finally, sulfur-carbon nanospheres (CNs) were used as the adsorbent to remove Pb+2 ions from aqueous solutions because of the high surface area of S-CNs from CNs and N-CNs. The synthesized nanospheres were examined by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy, transmission electron microscopy (TEM), and nitrogen adsorption-desorption isotherms. The results show spherical shapes have a particle size of up to 65 nm with a high surface area capable of absorbing lead ions efficiently. Additionally, the factors affecting the process of adsorption that include equilibrium time, temperature, pH solution, ionic intensity, and adsorbent dose were studied. The equilibrium removal efficiency was studied employing Langmuir, Freundlich, and Temkin isotherm forms. The kinetic data were analyzed with two different kinetic models, and both apply to the adsorption process depending on the values of correlation coefficients. The thermodynamic parameters including Gibbs free energy (ΔG°), standard enthalpy change (ΔH°), and standard entropy change (ΔS°) were calculated for the adsorption process.

Selective adsorption of Ag (Ⅰ) from aqueous solutions using Chitosan/polydopamine@C@magnetic fly ash adsorbent beads

A Chitosan/polydopamine@C@magnetic fly ash (CPCMFA) adsorbent bead was prepared for adsorption of Ag (Ⅰ) in aqueous solutions and exhibited good selectivity for Ag (Ⅰ) ion. To investigate its adsorption behaviors, equilibrium, kinetic and selective studies were conducted through batch experiments. Additionally, the influence of the pH value was also evaluated. In addition, the nature, composition, morphology, and magnetic property of the prepared adsorbent beads were characterized by Fourier transform-infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) analysis, thermogravimetric-differential scanning calorimetry (TG-DSC) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating-sample magnetometry (VSM). The freeze-dry form of CPCMFA also exhibited high adsorption capacity and selectivity for Ag (Ⅰ), with a maximum adsorption capacity of 57.02 mg/g at pH 4 and 30 °C. The experimental data were well described by the Langmuir isotherm and elovich kinetic models. The thermodynamics parameters, ΔH = 10.653 kJ/mol, ΔS = 96.63 J/mol K and ΔG < 0, demonstrate that the adsorption of Ag (Ⅰ) on the freeze-dry form adsorbent is spontaneous and endothermic. Moreover, regeneration studies showed the high recyclability of the adsorbent, which after five cycles of use it was still able to adsorb 95.7% of the amount adsorbed by the fresh adsorbent.

The efficient removal of methylene blue from water samples using three-dimensional poly (vinyl alcohol)/starch nanofiber membrane as a green nanosorbent

In the present study, a simple, fast, and economical method was introduced to eliminate methylene blue from dye wastewater water using a non-toxic, inexpensive, stable, and efficient adsorbent. The poly (vinyl alcohol) (PVA)/starch hydrogel nanofiber membrane with high surface area and the three-dimensional structure was fabricated in water via electrospinning strategy, and the cross-linking reaction was done by thermal treatment. The characterization of the nanofibers was carried out using Fourier-transform infrared spectrometer (FT-IR) and field-emission scanning electron microscopy (FE-SEM), and the cross-linked PVA/starch nanofiber was applied as a membrane for the removal of methylene blue (MB). The recovery of MB was performed by methanol solution containing 5% (v/v) HCl. Langmuir isotherm model successfully described the adsorption of MB on nanosorbent, and the maximum adsorption capacity (q_m) was 400 mg g^-1. Also, the kinetic of adsorption was well fitted by the pseudo-second-order model. In this study, because of the high stability of fabricated membrane (based on the tensile testing), it can be used as a filter for the fast separation of MB (cationic dye) and methyl orange (MO, anionic dye). Graphical abstract.

Polyethylenimine modified potassium tungsten oxide adsorbent for highly efficient Ag+ removal and valuable Ag0 recovery

Elemental Ag⁰ is well known for its remarkable catalytic and antibacterial properties, thus the regeneration of valuable Ag⁰ metal from Ag⁺ wastewater is of great significance. In this study, a novel polyethylenimine (PEI) modified potassium tungsten oxide (N-K₂W₄O₁₃) adsorbent was prepared for Ag⁺ removal and reduction to Ag⁰ using glutaraldehyde as crosslinking agent. XPS and FT-IR spectra verified PEI successfully anchored on the surface O and W atoms of K₂W₄O₁₃ through aldehyde bridges. The content of PEI in N-K₂W₄O₁₃ was calculated as 8.74wt% by TG curve. A heterogeneous PEI coating was observed in the SEM and TEM images. The N-K₂W₄O₁₃ exhibited larger Ag⁺ uptake (48.25mg/g) than the raw K₂W₄O₁₃ (42.50mg/g) though required a longer equilibrium time. This was due to the combined results of strong chelation and weak electrostatic repulsion that meanwhile occurring on the positive-charged surface of N-K₂W₄O₁₃. The maximum Ag⁺ uptake on N-K₂W₄O₁₃ was 72.5mg/g, which was larger than many of the reported adsorbents. Furthermore, the prepared N-K₂W₄O₁₃ displayed good anti-interference toward background ions (Na⁺, K⁺) and hold a stable Ag⁺ removal (>95%) after five runs of recycling tests. The mechanism studies elucidated that NH/N groups from the PEI modified N-K₂W₄O₁₃ mainly accounted for the Ag⁺ adsorption and Ag⁰ recovery in the adsorption-reduction process. Ion-exchange between Ag⁺ and K⁺ from the N-K₂W₄O₁₃ lattice also occurred. This work provided a facile method to synthesize a promising adsorbent for Ag⁺ wastewater remediation and valuable Ag⁰ recovery.

Exploratory of immobilization remediation of hydroxyapatite (HAP) on lead-contaminated soils

This study was aimed to investigate the adsorption and fixation effects of hydroxyapatite (HAP) on lead-contaminated soil. According to the experimental results, the microstructure of hydroxyapatite was observed by a scanning electron microscope (SEM). Fourier transform infrared spectroscopy (FTIR) showed that OH^- and PO₄^3- were the main functional groups in HAP. Optimum adsorption conditions of Pb²⁺ were obtained: 0.2 g/L, adsorbent; initial solution pH of 5.5; and contact time of 120 min. The kinetic adsorption experiments were carried out with the initial lead solution concentrations of 50 mg/L, 150 mg/L, and 250 mg/L. The kinetics fitting was consistent with the pseudo-second-kinetic model, which indicated that the main process of HAP adsorption of Pb²⁺ was mainly controlled by surface reactions and chemical reactions. The adsorption isotherms had a satisfactory fit with the Langmuir model, which indicated that the adsorption of Pb²⁺ by HAP was a monolayer adsorption. According to the experimental results, ion exchange, phosphorus supply, precipitate, and complexation are the main immobilization mechanisms for soil remediation with HAP. In remediation of Pb²⁺-contaminated soil experiments, the adsorption rate of Pb²⁺ by HAP was significantly higher than that of non-HAP soil with increasing immobilization days. With the increasing addition of HAP, the weak acid soluble (WA), reducible (RED), oxidizable (OX), and water soluble (WS) are transformed into residue (RES). The application of HAP in contaminated soil effectively reduced the leachable and exchangeable Pb²⁺, indicating that HAP is a potential material for remediating environmental pollution with Pb²⁺.

Graphene oxide mediated reduction of silver ions to silver nanoparticles under environmentally relevant conditions: Kinetics and mechanisms

We systematically investigated the reduction mechanisms and reduction kinetics of silver ions (Ag ions) by graphene oxide (GO) under ambient condition. UV-vis spectroscopy, transmission electron microscopy, and electron diffraction results revealed that silver nanoparticles (Ag NPs) could be formed from aqueous Ag ions in the presence of GO at pH 8 under light. Formation of Ag NPs increased with increasing pH (7.4, 8, and 9) and temperature (from 30 to 90); however, the increasing ionic strength and dissolved oxygen reduced the Ag NPs yield. The Ag ions reduction by GO followed pseudo-first-order kinetics under both dark and light, and light irradiation significantly accelerated the Ag NPs formation induced by GO. The phenolic-OH on GO was the dominating electron donator for Ag ion reduction in dark. Exposure to light increased the concentration of phenolic-OH on the GO surface, thereby stimulating the reduction rate of Ag ions by GO. In addition, the light induced electron-hole pairs on GO surface and light activated oxygen-centered radicals on GO surface promoted the reduction of adsorbed Ag ions by GO. Our findings provide important information for the role of GO in reducing Ag ions to Ag NPs in aquatic environments, and shed light on understanding the environmental fate and risk of both Ag ions and GO materials.

High-performance carbon/MnO2 micromotors and their applications for pollutant removal

The wide applications of particulate micromotors in practice, especially in the removal of environmental pollutants, have been limited by the low production yields and demand on high concentration of fuel such as H₂O₂. Carbon/MnO₂ micromotors were made hydrothermally using different carbon allotropes including graphite, carbon nanotube (CNT), and graphene for treatment of methylene blue and toxic Ag ions. The obtained micromotors showed high speed of self-propulsion. The highest speed of MnO₂-based micromotors to date was observed for CNT/MnO₂ (>2 mm/s, 5 wt% H₂O₂, 0.5 wt% surfactant). Moreover, different from previous studies, even with low H₂O₂ concentration (0.5 wt%) and without surfactant addition, the micromotors could also be well dispersed in water by the O₂ stream released from their reaction with H₂O₂. The carbon/MnO₂ micromotors removed both methylene blue (>80%) and Ag ions (100%) effectively within 15 min by catalytic decomposition and adsorption. Especially high adsorption capacity of Ag (600 mg/g) was measured on graphite/MnO₂ and graphene/MnO₂ micromotors.

3D carbon nanosphere and gold nanoparticle-based voltammetric cytosensor for cell line A549 and for early diagnosis of non-small cell lung cancer cells

An electrochemical cytosensor for the detection of the non-small-cell lung cancer cell line A549 (NSCLC) had been developed. A microwave-hydrothermal method was employed to prepare monodisperse colloidal carbon nanospheres (CNSs). Gold nanoparticles (AuNPs) were placed on the surface of the colloidal CNSs by self-assembly to obtain 3D-structured microspheres of the type CNS@AuNP. The results of an MTT assay show the microspheres to possess good biocompatibility. The CNS@AuNP nanocomposite was then placed, in a chitosan film, on a glassy carbon electrode (GCE). The voltammetric signals and detection sensitivity are significantly enhanced owing to the synergistic effect of CNSs and AuNPs. A cytosensor was then obtained by immobilization of antibody against the carcinoembryonic antigen (which is a biomarker for NSCLC) on the GCE via crosslinking with glutaraldehyde. Hexacyanoferrate is used as an electrochemical probe, and the typical working voltage is 0.2 V (vs. SCE). If exposed to A549 cells, the differential pulse voltammetric signal decreases in the 4.2 × 10^-1 to 4.2 × 10^-6 cells mL^-1 concentration range, and the detection limit is 14 cells mL^-1 (at S/N = 3). Graphical abstract Schematic presentation of design strategy and fabrication process of the electrochemical cytosensor for A549 cells. (CNS: carbon nanospheres; GA: glutaraldehyde; PEI: polyethyleneimine; AuNPs: gold nanoparticles; BSA: Bovine serum albumin).