Adsorption and Reduction from Modified Polypyrrole Enhance Electrokinetic Remediation of Hexavalent Chromium-Contaminated Soil

Heavy metal pollutant Cr(Ⅵ) in the environment will pose a severe threat to animal and human health. In this work, Fe3O4@PPy, Arg@PPy, and Arg/Fe3O4@PPy were prepared to enhance adsorption of Cr(Ⅵ) by doping Fe3O4 nanoparticles and amino radicals into the original PPy structure. Their characteristics were investigated by FTIR, SEM, EDS, BET analysis, and batch adsorption experiments. And they were used as permeable reaction barriers (PRB) to combine with electrokinetic remediation (EKR) to remediate Cr-contaminated soil. Adsorption experiment results showed that the maximum adsorption capacities of PPy, Fe3O4@PPy, Arg@PPy, and Arg/Fe3O4@PPy for Cr(Ⅵ) were 60.43 mg/g, 67.12 mg/g, 159.86 mg/g, and 141.50 mg/g, respectively. All of them followed the kinetic pseudo-second-order model and the Langmuir isothermal model with a monolayer adsorption behavior. In EKR/PRB system, the presence of Fe3O4@PPy, Arg@PPy, and Arg/Fe3O4@PPy obtained the higher Cr(Ⅵ) removal efficiency near the anode than that of the PPy, increasing by 74.60%, 26.04%, 68.64%, respectively. A strong electrostatic attraction between anion contaminants and protonated modified PPy and a reduction from Cr(Ⅵ) to Cr(Ⅲ) appeared in the EKR remediation process under acid conditions. This study opened up a prospect for applying modified PPy composites to treat heavy metal contaminated soil.

Removal of rhodamine B from aqueous solution by adsorption on corn cobs activated carbon

<p>In the present study, adsorption experiments were carried out to investigate the removal of rhodamine B from an aqueous solution using chemically activated carbon from corn cobs, a cheaper adsorbent. The characteristics of carbon were determined using X-ray diffraction, SEM, iodine number, pHpzc, and the Boehm titration method. The results show that the prepared activated carbon is amorphous, microporous, and generally acidic on the surface. The kinetic study of the adsorption of rhodamine B on this carbon was carried out, and the rate of sorption was found to conform to pseudo-second-order kinetics with 80 min as equilibrium time. The equilibrium adsorption revealed that the experimental data fitted better to the Langmuir isotherm model for removing rhodamine B. The interaction rhodamine B-activated carbon is mainly chemisorption type. The optimal conditions of rhodamine B removal onto the carbon of this study are mass of carbon = 0.3 g and pH = 3.15. The maximum monolayer adsorption capacity for rhodamine B removal was found to be 5.92 mg.g^-1. This study has shown that the prepared activated carbon makes it possible to effectively clean up wastewater contaminated by rhodamine B with a removal efficiency of up to 99.60% for 300 mg of AC in 25 mL of the rhodamine B solution (5 mg.L^-1).</p>

Iron-Loaded Carbon Aerogels Derived from Bamboo Cellulose Fibers as Efficient Adsorbents for Cr(VI) Removal

A unique iron/carbon aerogel (Fe/CA) was prepared via pyrolysis using ferric nitrate and bamboo cellulose fibers as the precursors, which could be used for high-efficiency removal of toxic Cr(VI) from wastewaters. Its composition and crystalline structures were characterized by FTIR, XPS, and XRD. In SEM images, the aerogel was highly porous with abundant interconnected pores, and its carbon-fiber skeleton was evenly covered by iron particles. Such structures greatly promoted both adsorption and redox reaction of Cr(VI) and endowed Fe/CA with a superb adsorption capacity of Cr(VI) (182 mg/g) with a fast adsorption rate (only 8 min to reach adsorption equilibrium), which outperformed many other adsorbents. Furthermore, the adsorption kinetics and isotherms were also investigated. The experiment data could be much better fitted by the pseudo-second-order kinetics model with a high correlating coefficient, suggesting that the Cr(VI) adsorption of Fe/CA was a chemical adsorption process. Meanwhile, the Langmuir model was found to better describe the isotherm curves, which implied the possible monolayer adsorption mechanism. It is noteworthy that the aerogel adsorbent as a bulk material could be easily separated from the water after adsorption, showing high potential in real-world water treatment.

Removal of Trimethoprim from Water using Carbonized Wood Waste as Adsorbents

Daniellia—oliveri sawdust-based adsorbents were employed to remove trimethoprim (TMP) from water. The sawdust was thermally carbonized and activated in-stu with ZnCl2 and H3PO4 separately. The adsorbents surface features were profiled using scanning electron microscopic (SEM) and pH point of zero charge (pHpzc ) analyses. The prospects of the adsorbents for the removal of trimethoprim from water were verified. The adsorption processes were performed under different experimental conditions. The adsorption isotherm, the kinetics, and the thermodynamics were studied; and the data fitting output revealed that both chemisorptions and physisorption occurred. Surface and pore diffusion played active role in the adsorption of TMP by the adsorbents. The optimum conditions for adsorption of TMP by the adsorbents were pH at slightly acidic to neutral medium and temperature at room temperature. The fitting isotherm models were: Langmuir (R2 = 0.993) for the zinc-chloride-activated-carbon, Temkin (R2 = 0.962) for the phosphoric-acid-activated-carbon, and the kinetics: pseudo-second order (R2 = 0.997) for both. The maximum monolayer adsorption capacities of the adsorbents for TMP was 4.115 and 6.495 mg/g, respectively. The thermodynamic parameters determined suggested feasibility, spontaneity, and endothermicity of the adsorption processes. The results reveal that the adsorbents were goodprospects for the removal of TMP from water.

Biosorption of Chromium by Agricultural Waste, Anacardium Occidentale Testa Powder: Characterization, Kinetic, Isotherm and Thermodynamic Studies

The study on low-cost biosorbent such as Anacardium occidentale testapowder was used to remove chromium from aqueous solutions. Based on R 2 values, the Langmuir (R 2 = 0.9927) model fitted the equilibrium biosorption data best, confirming monolayer adsorption of chromium on to the biosorbent surface. The biosorption of chromium was best described by pseudo-second order (R 2 =0.9902) kinetics since at all concentrations, the R 2 values were higher than the corresponding pseudo-first order (R 2 = 0.9278) values. Based on thermodynamic parameters the biosorption of chromium by Anacardium occidentale testa powder was found to be spontaneous, endothermic and feasible under optimized conditions.

Study on synthesis and adsorption property of porous carbon/Ni nanoparticle composites

The porous carbon/Ni nanoparticle composite was prepared by a freeze-drying method using NaCl as the template. It was applied in the effect of the concentration, adsorption time, and temperature of adsorption on the adsorption behavior. The kinetic model and the adsorption isothermic fitting results show that the adsorption behavior fits with the pseudo-secondary dynamics and the Langmuir isothermal model, indicating that the adsorption process is monolayer adsorption. Thermodynamic results indicate that the adsorption process is spontaneous physicochemical adsorption. The fitting showed that the porous carbon/Ni nanoparticle composites reach 217.17 mg·g-1, at 313 K indicates good adsorption for Congo red.

Enanced removal of scaling cations from oilfield produced water by carrier mineral floatation

This work reports a novel carrier flotation protocol for removing scaling cations from an oilfield produced water source which significantly reduces the collector consumption by employing natural minerals such as quartz, montmorillonite and talcum as the scaling cations carriers. The scaling cations uptake onto all carrier minerals exhibited homogeneous and monolayer adsorption, which was mainly dominated by physisorption. After adding oleate collector, the scaling cations removal rate was further enhanced, which was attributed to its high affinity with the scaling cations. Notably, the talcum flotation process simultaneously offered high scaling cations removal rate (76.1%) and mineral recovery rate (98.3%), which achieved a sediment yield reduction of 72.2%. By summarizing the characterization results, the scaling cations removal mechanisms were also proposed. Moreover, high regeneration efficiencies (86.1% and 84.8% for quartz and talcum regeneration within 3 cycles) were achieved by the proposed regeneration protocol. This carrier flotation protocol with its low collector consumption offered technical promise for scaling cations removal from oilfield produced water.

Contamination Control for Ultra-Sensitive Life-Detection Missions

A key science priority for planetary exploration is to search for signs of life in our Solar System. Life-detection mission concepts aim to assess whether or not biomolecular signatures of life are present, which requires highly sensitive instrumentation. This introduces greater risk of false positives, and perhaps false negatives. Stringent science-derived contamination requirements for achieving science measurements on life-detection missions necessitate mitigation approaches that minimize, protect from, and prevent science-relevant contamination of critical surfaces of the science payload and provide high confidence to life-detection determinations. To this end, we report on technology advances that focus on understanding contamination transfer from pre-launch processing to end of mission using high-fidelity physics in the form of computational fluid dynamics and sorption physics for monolayer adsorption/desorption, and on developing a new full-spacecraft bio-molecular barrier design that restricts contamination of the spacecraft and instruments by the launch vehicle hardware. The bio-molecular barrier isolates the spacecraft from biological, molecular, and particulate contamination from the external environment. Models were used to evaluate contamination transport for a designs reference mission that utilizes the barrier. Results of the modeling verify the efficacy of the barrier and an in-cruise decontamination activity. Overall mission contamination tracking from launch to science operations demonstrated exceptionally low probability on contamination impacting science measurements, meeting the stringent contamination requirements of femtomolar levels of compounds. These advances will enable planetary missions that aim to detect and identify signatures of life in our Solar System.

A Comparative Study on Hexavalent Chromium Adsorption onto Chitosan and Chitosan-Based Composites

Chitosan (Cs)-based composites were developed by incorporating silica (Cs–Si), and both silica and hydroxyapatite (Cs–Si–Hap), comparatively tested to sequester hexavalent (Cr(VI)) ions from water. XRD and FT-IR data affirmed the formation of Cs–Si and Cs–Si–Hap composite. Morphological images exhibits homogeneous Cs–Si surface, decorated with SiO2 nanoparticles, while the Cs–Si–Hap surface was non-homogeneous with microstructures, having SiO2 and Hap nanoparticles. Thermal analysis data revealed excellent thermal stability of the developed composites. Significant influence of pH, adsorbent dose, contact time, temperature, and coexisting anions on Cr(VI) adsorption onto composites was observed. Maximum Cr(VI) uptakes on Cs and developed composites were observed at pH 3. The equilibration time for Cr(VI) adsorption on Cs–Si–Hap was 10 min, comparatively better than Cs and Cs–Si. The adsorption data was fitted to pseudo-second-order kinetic and Langmuir isotherm models with respective maximum monolayer adsorption capacities (qm) of 55.5, 64.4, and 212.8 mg/g for Cs, Cs–Si, and Cs–Si–Hap. Regeneration studies showed that composites could be used for three consecutive cycles without losing their adsorption potential.

ECOFRIENDLY ADSORBENT FROM FOOD WASTE FOR WATER PURIFICATION

Egg shell, which is a waste material emerging out in large quantities from poultries, homes and restaurants, may be used as a good adsorbent for heavy metals. Different types of eggshells were used in this study for the adsorption of a major pollutant such as iron from surface water. Effect of CaCO3 content in the egg shell, particle size, contact time, temperature and shaking on adsorption were also studied. The adsorption isotherms fitted by the Langmuir model revealed that the adsorption of iron by eggshell samples was monolayer adsorption.