Green Adsorbent Research Articles

Potential use of Thai mango (Mangifera indica Linn. cultivar Chok-Anan) seed porous starch for retention of aroma compounds from coffee extract

This study aimed to extract and modify the properties of the starch from Thai mango seeds (cultivar Chok-Anan). The porous starch samples were obtained using enzymatic treatment and its potential to retain aroma compounds from coffee extract was evaluated. The physicochemical properties, structure characteristics, porosity characteristics and adsorption quantity of starches were also determined. The retention of coffee aroma compounds was investigated through combining starch or porous starch with odorants, and storing the mixtures at room temperature for 7 and 14 days, respectively. The chemical properties of aroma compounds as well as starch surface properties were observed to affect the retention of aroma compounds upon storage. Additionally, 2-furanmethanol, d-limonene and maltol were selected to be the primary target compounds to assess the retention of odorants. This study observed a noticeable decrease in d-limonene content throughout the storage period. On the contrary, after 14 days of storage, the porous starch exhibited high retention of hydroxy compounds including 2-furanmethanol and maltol. However, after prolonged storage their ability to retain 2-furanmethanol and maltol slightly decreased. Therefore, the porous starch derived from mango seeds exhibited the potential to retain coffee aroma compounds and could be a desirable green adsorbent for food and cosmetic industries.

Remediation of Cr(VI) using a radiation functionalized green adsorbent: Adsorption modelling, mechanistic insights and prototype water purifier demonstration

The work reports remediation of hexavalent Chromium (Cr(VI)) in water using a radiation functionalized cellulose based green adsorbent, fabricated via gamma radiation assisted Mutual Irradiation Grafting Process (MIGP), wherein poly(2-Trimethylammoniumethyl methacrylate chloride) (PTMAEMC) was grafted onto Woven Cotton Cellulose Fabric (WCCF). The grafted adsorbent “ChromClear” efficiently sequestered Cr(VI) from water and demonstrated a maximum adsorbent capacity of ∼55 mg.g−1, successfully curtailing Cr(VI) concentrations to <20 μg.L−1. Characterization of samples was performed using 13C NMR, XPS, SEM-EDS, FTIR, TGA, and BET analysis. The equilibrium adsorption, kinetic, and breakthrough curve data were analysed using various theoretical models to infer the adsorption mechanism and extract important process parameters. Artificial Neural Network (ANN) modelling was used to predict adsorption capacity and % Cr(VI) removal in continuous flow column mode under different operational conditions, with a high degree of agreement (R2 > 0.99) between experimental and modelled data. Density Functional Theory (DFT) calculations established the interaction between CrO42− and PTMAEMC groups of ChromClear to be occurring in a 1:2 ratio. ChromClear could be regenerated for over five recycled iterations with >88 % retention in adsorption capacity. Concept based prototype water purification systems were also developed for pump as well as gravity driven continuous flow operations, and successfully demonstrated for remediation of Cr(VI) contaminated ground water samples. The efficacy and simplicity of the process provides ample scope for further upscaling and deployment for community level water treatment applications, with a special emphasis on compliance with drinking water norms in affected areas.

Modified hemp fibers as a novel and green adsorbent for organic dye adsorption: adsorption, kinetic studies and modeling

Synthetic dyes represent a serious hazard to aquatic environments. Many approaches for eliminating these contaminants have been devised and applied. This manuscript reports the production of a novel, low-cost and ecologically friendly bioadsorbent based on hemp fibers that are functionalized with graphite oxide through bridging with an organosilane. Methylene blue was selected as a typical pollutant to be removed from wastewaters. The adsorbent was characterized through scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and Fourier-transform infrared (FTIR) analysis. An investigation of the effects of pH and temperature on the adsorption process was carried out. The adsorption capacity increased with increasing contact time as well as with the temperature, proving that the process shows endothermic behavior. Moreover, the process was found to be dependent on the pH level and, to corroborate the collected results, the point of zero charge was evaluated. The maximum adsorption capacity was found to be 57 mg/g, which was achieved with the following parameters: pH = 7.5, T = 80 °C and an initial dye concentration equal to 5 mg/L. Reusability studies showed a 15% decrease in adsorption capacity after 30 adsorption tests, proving the possibility of reusing the produced adsorbent without any great decay in performance. Finally, a potential adsorption mechanism is reported and discussed. The reported results prove that it is feasible to apply the designed adsorbent of organic dyes to the purification of wastewaters.Graphical abstract

Smart Sorption: Novel applications of cellulosic nanomaterials for selective critical metal recovery from black mass leachates through multibatch processes

Selective critical metal recovery from black mass leachates (BML) is a great challenge for the Li-ion batteries recycling sector. This paper shows the potential of nanocellulose products as green adsorbents for a selective recovery of critical metals through multibatch sorption processes. Cellulose nanocrystals (CNCs) and cellulose nanofibers (CNFs) of 0.4 and 1.5 meq/g cationic demand, respectively, have been produced and used as biosorbents. Metal leaching from non-pyrolyzed black mass with HCl presented the highest critical metal extraction yield, obtaining up to 10 g/L of Co and more than 1 g/L of Cu, Mn and Ni. The adsorbents were tested under different dosages and pH conditions for the treatment of both synthetic multimetal solution (MMS), with Mn, Cu, Co, and Ni, and real BML, through a multiple step batch treatment to increase the selectivity towards each critical metal. For MMS treatments, the lowest pH (1–2) conditions are favorable for Co separation, reaching 135 g/g, while higher pH values (4–5) are better to recover Cu and Ni. Selectivity indexes between metals could reached values above 40 for the optimal conditions. For the treatment of BML, pH around 3 enhanced the selectivity of Al and pH of 5 of the Li. In this case, metal recoveries were higher than 30 g/g. When CNCs were used, more than 4 g/g of Co was adsorbed, recovering more than 99 % of the Co present in the waste. 99 % of Co purity was obtained at the optimal Co selective recovery conditions. Although the studied critical metals were strongly sorbed onto the nanocelluloses, a solution with a concentration of 2.5–5 g/L of these metals could be extracted from desorption tests.

Removal of Cr(VI) from aqueous solution using ball mill modified biochar: multivariate modeling, optimization and experimental study

Chromium (Cr(VI)) pollution has attracted wide attention due to its high toxicity and carcinogenicity. Modified biochar has been widely used in the removal of Cr(VI) in water as an efficient and green adsorbent. However, the existing biochar prepared by chemical modification is usually complicated in process, high in cost, and has secondary pollution, which limits its application. It is urgent to explore modified biochar with simple process, low cost and environmental friendliness. Therefore, ball milling wheat straw biochar (BM-WB) was prepared by ball milling technology in this paper. The adsorption characteristics and mechanism of Cr(VI) removal by BM-WB were analyzed by functional group characterization, adsorption model and response surface method. The results showed that ball milling effectively reduced the particle size of biochar, increased the specific surface area, and more importantly, enhanced the content of oxygen-containing functional groups on the surface of biochar. After ball milling, the adsorption capacity of Cr(VI) increased by 3.5–9.1 times, and the adsorption capacity reached 52.21 mg/g. The adsorption behavior of Cr(VI) follows the pseudo-second-order kinetics and Langmuir isotherm adsorption model rate. Moreover, the Cr(VI) adsorption process of BM-WB is endothermic and spontaneous. Under the optimized conditions of pH 2, temperature 45 °C, and adsorbent dosage 0.1 g, the removal rate of Cr(VI) in the solution can reach 100%. The mechanism of Cr(VI) adsorption by BM-WB is mainly based on electrostatic attraction, redox and complexation. Therefore, ball milled biochar is a cheap, simple and efficient Cr(VI) removal material, which has a good application prospect in the field of remediation of Cr(VI) pollution in water.

Enhanced biosorptive incarceration of nitrate from aqueous solutions using novel green adsorbent: Performance optimization and mechanistic enlightenment

Excess nitrate contamination was lucratively addressed using the novel adsorbents prepared from waste seed pods of the Guilandina bonduc (L.) plant. Adsorbents BFP and EBFP (amino-grafted) were synthesized following a green pathway of thermo-chemical transformation. Adsorbents were successfully implemented for nitrate adhesion from natural and wastewater. The morphology of the adsorbents was studied using SEM-EDS, TGA, XRD, FTIR-ATR, and BET, including zeta potential and point of zero charges. The batch mode nitrate removal study was carried out using a colorimeter. The optimum efficiency in nitrate trapping was found to be 173.8 mg/g (EBFP) and 78.74 mg/g (BFP). The adsorption efficiency of the sorbents was further optimized using the RSM-CCD and found to be suitable. The batch sorption study was also supported by the column study with a breakthrough curve at 90% (EBFP) and 60% (BFP) for the regeneration study. The optimum value for EBFP was attained at an initial nitrate concentration of 110 mg/L, pH∼8, and a dosage of 12 g/L at room temperature within 75 minutes of contact. The Freundlich isotherm model and pseudo-second-order kinetics fit satisfactorily with the sorption trends followed by other isotherm and kinetic models. The influence of various competing ions e.g., PO43−, Cl−, HCO3−, SO42−etc., on nitrate adsorption study was investigated. The physicochemical sorption of nitrate was confirmed, and a plausible mechanism has been suggested accordingly. The field sample experiment, including the start-up opportunities with this work, has been highlighted. EBFP could be an excellent sorbent of choice at present that is ready for commercialization.

Tetraethylenepentamine-modified Cu2(OH)PO4 for efficient CO2 capture

This study focused on creating tetraethylenepentamine (TEPA) modified copper hydroxyl phosphate (Cu2(OH)PO4) adsorbents via physical impregnation. The TEPA-modified Cu2(OH)PO4 adsorbents were analyzed for structure and characteristics through SEM, XPS, TGA, N2 adsorption–desorption studies. The effects of different parameters (TEPA contents, temperatures, flow rates and CO2 concentrations) and cyclic stability were evaluated. Kinetics, thermodynamics and density functional theory (DFT) calculations were employed to understand the impact of TEPA modification on Cu2(OH)PO4 for CO2 adsorption. Experimental results showed that a 50 wt% loading yielded optimal results, with a maximum surface area of 65.12 m2/g, a pore volume of 0.29 cm3/g, and a maximum adsorption capacity of 6.54 mmol/g. The amine efficiency is extraordinary which reached 67 %. The best performance occurred at 60 °C, 30 ml/min gas flow, and 15 vol% CO2 concentration. The pseudo-second-order kinetic model better described the CO2 adsorption process. The adsorption process was found to be exothermic at 20–60 °C and endothermic at 60–80 °C, suggesting physical–chemical co-adsorption and chemical adsorption, respectively. The adsorption activation energy is 34.322 kJ/mol. The DFT shows the adsorption energy ranged from −0.565 eV to −5.584 eV, indicating coexistence of physical and chemical adsorption. The d-band theoretical calculation shows that TEPA doping is beneficial to the adsorption of CO2 by Cu2(OH)PO4. Minimal structural modification of the adsorbate was observed, with bond lengths changing by less than 1 %. The density of states (DOS) curve shifted toward lower-energy states after adsorption, suggesting a more stable structural configuration post-adsorption. We have proved that TEPA-Cu2(OH)PO4 has good adsorption for CO2 and is an efficient green adsorption material.

Composite Layered Double Hydroxide Zn-Al/Magnetic Biochar Modified for Highly Effective Malachite Green Adsorption

One of the main needs of humans is water, one source of water pollutantion is from dyes. Adsorption is the most popular method in removing pollutants as it is proven to be efficient. One of the dyes harmful to living things is malachite green. In this study, malachite green dye was removed using a layered double hydroxide (LDH) Zn-Al/magnetic biochar composite. The XRD, FTIR, BET, and VSM analyses show that the LDH Zn-Al, magnetic biochar, and LDH Zn-Al/magnetic biochar composite were successfully produced. The surface area of the Zn-Al/magnetic biochar composite made up of LDH increased from 9.621 m2/g to 99.473 m2/g. The point of zero charge of LDH Zn-Al and magnetic biochar were at pH 6, whereas the composite of these two materials was at pH 7. For LDH Zn-Al, magnetic biochar, and composite LDH Zn-Al/magnetic biochar, pH 8 is the ideal value for adsorption of malachite green. PSO (pseudo-second order) kinetics is the best-fit model. LDH Zn-Al, magnetic biochar, and LDH Zn-Al/magnetic biochar composite had adsorption capacities of 14.472, 15.552, and 25.907 mg/g, respectively, at a temperature of 60°C. Regeneration showed the LDH Zn-Al/magnetic biochar composite had superior and more effective ability compared to LDH Zn-Al and magnetic biochar.

PAN/PVP/CD-MOF Composite Beads for the Removal of Methylene Blue and Congo Red in Water

Cyclodextrin metal-organic frameworks (CD-MOFs) are synthesized from green precursors, making them an ideal material for green adsorbents. However, CD-MOFs are unstable in water, thus limiting their applications. Here, we report encapsulating CD-MOFs in polyacrylonitrile (PAN) and polyvinylpyrrolidone (PVP) polymeric support to produce PAN/PVP/CD-MOF composite beads. Batch adsorption studies showed that high dye adsorption capacities could be obtained at intermediate PVP, high PAN, and low CD-MOF loadings. Maximum MB and CR sorption capacities under optimum bead formulation: PAN = 6.96 wt.%, PVP = 2.20 wt.%, and CD-MOF = 2.88 wt.%. The optimized composite beads have a sorption capacity of 37.40 mg/g for MB and 18.42 mg/g for CR. We showed that PAN/PVP/CD-MOF composite beads could be an excellent adsorbent for textile dye removal in water.

Synthesis of a Green Adsorbent Surface Gels: Development of Ratio Preparation of Polymer SA/Bentonite Bead, and its Industrial Applications for Removal of Aqueous Pollutants

In this research, polymer gels sodium alginate/bentonite clay adsorbent beads (SA/Ben) were prepared via encapsulating natural bentonite (Bn) in sodium alginate (SA). The ratio of Polymer Gels SA/Bn was used during preparation bead to yield beads (1/1 w/w), SA-Bn2 (1/2 w/w), and SA-Bn3 (1/3 w/w), respectively. These adsorbents were characterized via different characterisation FESEM, TEM, XRD and EDX to give high confidence of the prepared surface. The adsorption of Clonazepam drug (CLZ) from aqueous solution on the SA/Bn beads was investigated as a function of different factors, including the initial concentration of CLZ, the weight of SA/Bn beads gel, pH solution, temperature of solution and equilibrium time. Adsorption models of Langmuir and Freundlich isotherms were applied and were found to be well described via the isotherm of Freundlich model. The results showed that among the three types of prepared surfaces SA/Bn beads, SA-Bn1 presented the greatest CLZ adsorption capacity. Thermodynamic parameters were calculated including change free of Gibbs energy (ΔG), change entropy (ΔS), and change enthalpy. The change enthalpy of CLZ drug adsorption was found to be positive for the SA/Bn bead and the reaction of adsorption spontaneous and exothermic. After the adsorption proses the SA/Bn beads can easily be regenerated via water and re-used within four cycles.

Adsorption of ethanol onto novel and indigenous green adsorbents: Synthesis, characterization, and applications

Adsorption refrigeration is considered the most promising cooling option, yet its commercialization is hindered by bulkiness and low performance due to the lack of suitable adsorbents. In India, crop residue management is a challenge because of the open-field burning of waste biomass that leads to global warming and health problems. Therefore, the present article focuses on developing and sustainable application of novel porous activated carbons (ACs) from abundantly available crop residues to address these issues. The ACs synthesized through KOH activation of optimized biochar, exhibited significant specific surface area of 2002 m2/g and 1241 m2/g with distinctive micro- and meso-pores for sugarcane bagasse (SBAC), and rice straw (RSAC), respectively compared to other. The surface morphology study provides the honeycomb structure as evidence of micropores developed during activation processes. The experimental data of ethanol uptake is best fitted to calculate the structural constants of the Dubinin-Astakhov (D-A) model. A new performance index known as the mass of adsorbent to combustion fuel ratio (mad/mcf) is proposed for the performance analysis of newly synthesized ACs as adsorbent with ethanol refrigerant in a renewable energy-powered adsorption cooling system (ACS). The SBAC-ethanol pair shows the highest effective uptake, and energy density of 0.535 kg/kg, and 612.24 kJ/kg, respectively at 80 °C and 4.28 kPa. Further, energy reduction potential evaluation for the newly prepared working pairs reveals a substantial decrease in energy input compared to composite-ethanol pairs from existing literature, indicating process improvements toward cleaner and more sustainable production. Thus, the present research underscores the proposed ACs as prime candidates for efficient and sustainable cooling and heat-pumping applications.

Plant-based calcium silicate from rice husk ash: A green adsorbent for free fatty acid recovery from waste frying oil

Driven by the urgent need for a solution to tackle the surge of rice husk (RH) and waste frying oil (WFO) waste accumulation at a global scale, this report highlights the use of calcium silicates (CS) extracted from acid-pre-treated rice husk ash (RHA) for free fatty acid (FFA) removal from WFO as conventional RHA shows limited FFA adsorption performance. A novel alkaline earth silicate extraction method from acid-pre-treated RHA was outlined. The structural and behavioural attributes of the synthesised CS were identified through BET, SEM-EDS, and XRD analyses and compared to those of RHA. Notable morphology and structural modification were determined, including reducing specific surface areas, mitigating from amorphous to crystalline structure with regular geometric forms, and detecting Si–O–Ca functional groups exclusive to CS adsorbents. A comparison study showed superior lauric acid (LA) adsorption performance by CS absorbents over acid-pre-treated RHA, with a significant increase from 0.0831 ± 0.0004 mmol LA/g to 2.5808 ± 0.0011 mmol LA/g after 60 min. Recognised as the best-performing CS adsorbent, CS-1.0 was used for further investigations on the effect of dosage, LA concentration, and temperature for efficient LA adsorption, with up to 100% LA removal and 5.6712 ± 0.0016 mmol LA/g adsorption capacity. The adsorption isotherm and kinetic studies showed LA adsorption onto CS-1.0 followed Freundlich isotherm with KF = 0.0598 mmol(1-1/n) L(1/n) g−1 & Qe,cal = 3.1696 mmol g−1 and intraparticle diffusion model with kid = 0.1250 mmol g−1 min0.5 & Ci = 0.9625 mmol g−1, indicating rapid initial adsorption and involvement of carboxylate end of LA and the calcium ions on the CS-1.0 in the rate-limiting step. The high equilibrium adsorption capacity and LA adsorption rate indicated that the proposed CS-1.0 adsorbent has excellent potential to recover FFA from WFO effectively.

Defluoridation of water through the application of carbonised bone as a green adsorbent: A review

Flouride contamination of water is recognised as a serious challenge facing humanity. Consumption of water that contains excessive amounts of fluoride can result in fluorosis. Consequently, concerted efforts have been made to develop cheap, effective and green techniques/materials to remove fluoride from water, particularly potable water. Bone char prepared from bovine, swine, and equine bones has been used extensively in this regard, and is the most promising, cheap and green material for treating drinking water with high fluoride concentration, particularly in developing countries. However, research on bone char prepared from bones of animals in the wild, as well as those from domestic and semi-wild animals treated with antibiotics to enhance growth, has been scanty. Such research is important as the use of antibiotics may alter the composition of bones, and thus their potential as a green adsorbent to remove fluoride may be impaired. Furthermore, little attempt has been made so far to package char bones for easy application domestically, particularly in rural communities. Significance: Contamination of water by fluoride is a major problem globally. Various techniques and materials have been employed for water defluoridation, including the use of bone char, which has several advantages. Bone char prepared from bones of animals in the wild and those from domestic and semi-wild animals treated with antibiotics to enhance growth should be further investigated. Cheaper and less elaborate processes and packaging are required to scale down the use of bone char at domestic level.

Citrus medica mediated Ag-doped MgO nanocomposites as green adsorbent and its catalytic performance in the rapid treatment of water contaminants

Citrus medica mediated Ag-doped MgO nanocomposites as green adsorbent and its catalytic performance in the rapid treatment of water contaminants

Green adsorbent for CO2 adsorption: MgO impregnated palm kernel shell-based activated carbon

Green adsorbent for CO2 adsorption: MgO impregnated palm kernel shell-based activated carbon

A review of recent trends in the removal of emerging contaminants from wastewater using green adsorbents

Water pollution caused by emerging contaminants (ECs) is perceived with deep concern nowadays due to their considerable impact and their persistence in wastewater treated using conventional methods. Pharmaceuticals, personal care items, and nanoparticles are examples of ECs that are increasingly utilized. Given that ECs pose a significant risk to human health and the environment, many wastewater treatment techniques have been developed in order to remove them. For instance, advanced wastewater treatments are highly effective at removing ECs but are expensive. Adsorption utilizing green adsorbents is a possible approach for finding a long-term, effective, and affordable solution to this issue. This review explores the efficiency of different green adsorbents applied in order to remove ECs from wastewater.

Acid-base reaction-based dispersive solid phase extraction of favipiravir using biotin from biological samples prior to capillary electrophoresis analysis.

In this study, an acid-base reaction-based dispersive solid-phase extraction method was developed for the extraction of favipiravir from deionized water, plasma and urine samples prior to its determination using a capillary electrophoresis-diode array detector. The target analyte was extracted from the samples using biotin as a green adsorbent. To reach this goal, the pH of the solution was first adjusted to 9.0 (using borate buffer), and the ionic strength of the solution was enhanced by adding sodium chloride (2.5%, w/v). Thereafter, an appropriate amount of biotin was dissolved in the solution and a homogenous phase was obtained. By adding hydrochloric acid to the solution, an acid-base reaction occurs via protonation of biotin, which decreases its solubility. During this procedure, the analyte was adsorbed onto the tiny particles of the produced adsorbent dispersed into the solution. The resulting mixture was sonicated to facilitate the adsorption of the analyte onto the adsorbent surface. After the collection of biotin particles through centrifugation, the analyte was eluted using acetonitrile and then used in the determination stage. Under the optimal extraction conditions, the calibration curve was linear from 250 to 3000 ng mL-1 with a coefficient of determination of 0.9968. Low limit of detection, and quantification, good repeatability on the same day and different days (relative standard deviation ≤ 8.2%), and acceptable extraction recovery were accessed. The applicability of the method was examined by performing it on spiked plasma and urine samples, and its performance was verified.

Use of Placuna placenta Shells as Green Adsorbent for Pb(II) Ions Sequestration from Aqueous Solution

&lt;p&gt;Heavy metal treatment is crucial to mitigate these elements' adverse environmental impacts. Among various remediation methods, adsorption stands out due to its simplicity and high efficiency. In this context, &lt;em&gt;Placuna placenta &lt;/em&gt;shell, a biowaste, has been explored for its potential in treating wastewater contaminated with Pb(II) ions. This research was designed to assess the &lt;em&gt;Placuna placenta &lt;/em&gt;shell's proficiency in removing Pb(II) ions from aqueous solutions. The study involved two main components: an adsorption test to evaluate the heavy metal removal capability of the &lt;em&gt;Placuna placenta &lt;/em&gt;shel and a comprehensive characterization of the shell-based adsorbent. The adsorption experiments were conducted using a batch system, where variables such as pH levels and contact time were meticulously altered to determine their effect on the adsorption efficiency. Concurrently, the adsorbent underwent thorough characterization through Fourier-Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD) analysis. The experimental findings indicated that the optimal conditions for maximum Pb(II) ion removal were achieved at a pH of 7 and a contact time of 120 minutes. The FTIR analysis of the adsorbent revealed the presence of calcium carbonate (CaCO&lt;sub&gt;3&lt;/sub&gt;), a finding further substantiated by the XRD analysis results. Additionally, SEM imaging provided visual evidence of metal ion deposition on the aggregates of the adsorbent. The study demonstrated that the &lt;em&gt;Placuna placenta &lt;/em&gt;shell exhibits promising qualities as an adsorbent for removing heavy metals from contaminated water sources. This finding highlights the potential of utilizing biowaste in environmental remediation and offers a sustainable approach to addressing heavy metal pollution.&lt;/p&gt;

Composite starch films as green adsorbents for removing benzo[a]pyrene from smoked sausages

Benzo[a]pyrene (BaP), which is emitted during the processing of smoked sausages, accumulates in sausages and poses a serious threat to human health. This study focused on the removal of BaP from sausages and accompanying particulate matter (PM) during the smoking of sausages by films formed by combining corn starch (CS) with K-carrageenan (KC)/sodium alginate (SA). Initially, the effects of different additions of KC and SA on the rheological analysis, thermogravimetric analysis (TGA) and film-forming properties of the composite films were investigated. The BaP reduction capacities of CS-KC and CS-SA composite films in sausage were 41.1%-47.0% and 54.2%-56.5%, respectively, because the three-dimensional mesh structure of the composite films provided a large number of adsorption sites. Finally, kinetic studies demonstrated that BaP control in composite films is mainly achieved by intraparticle diffusion. Therefore, due to its excellent recyclability and biodegradability, composite starch film has a promising application in smoked meat products.

Development of innovative and green adsorbents for in situ cleanup of fluoride-polluted groundwater: Mechanisms and field-scale studies

In this study, the magnesium oxide (MgO)-based adsorbents [granulated MgO aggregates (GA-MgO) and surface-modified MgO powder (SM-MgO)] were developed to remediate a fluoride-contaminated groundwater site. Both GA-MgO and SM-MgO had porous, spherical, and crystalline structures. Diameters for GA-MgO and SM-MgO were 1–1.7 mm and 1–10 μm, respectively. The pseudo second-order dynamic adsorption and the Freundlich isotherm could be applied to express the chemical adsorption phenomena. The monolayer adsorption was the dominant mechanism at the initial adsorption period. During the latter part of fluoride adsorption, the multilayer adsorption became the dominant mechanism for fluoride removal from the water phase, which also resulted in the increased adsorption capacity. Higher hydroxide, phosphate, and carbonate concentrations caused a decreased fluoride removal efficiency due to the competition of sorption sites between fluoride and other anions with similar electronic properties. Fluoride removal mechanism using GA-MgO and SM-MgO as the adsorbents was mainly carried out by the chemical adsorption. Reaction paths contained two main processes: (1) formation of magnesium hydroxide after the reaction of MgO with water, and (2) the hydroxyl group of the magnesium hydroxide was replaced by fluoride ions to form magnesium fluoride precipitation. Results from column tests show that up to 61 and 73% of fluoride removal (initial fluoride concentration = 9.3 mg/L) could be obtained after 50 pore volumes of groundwater pumping with GA-MgO and SM-MgO injection, respectively. The GA-MgO system could be applied to contain and remediate fluoride-contaminated groundwater, and SM-MgO could be applied as an immediate fluoride removal alternative to achieve a rapid pollutant removal for emergency responses. Up to 71% of fluoride removal (fluoride concentration = 10.8 mg/L) could be obtained with GA-MgO injection after 30 days of operation. The developed GA-MgO system is a potential and green remediation alternative to contain the fluoride plume significantly.