Modification Of Ferroferric Oxide/Peanut Husk Composites And Adsorption Property Of Materials Toward Typical Pollutants

The presence of pollutants in water significantly affects water quality as well as organisms that depend on water for survival.This coupled with the challenges associated with the ineffective management of agricultural waste materials in recent times have been a source of major concern to environmental scientist and the general public.Therefore,the utilization of waste biomass for the design and development of an adsorbent for wastewater treatment offers significant benefit to the environment,society and economy.Herein,novel adsorbents based on magnetic peanut husk were developed via the chemical modification process.In the design process,peanut husk was impregnated with Fe₃O₄particles and subsequently functionalized with either iminodiacetic acid（IDA）,polyethyleneimine（PEI）or betaine（Bet）.The efficiency of these novel adsorbents（labelled as PN-Fe₃O₄-IDA,PN-Fe₃O₄-IDA-Fe,PN-Fe₃O₄-IDA-Zr,PN-Fe₃O₄-IDA-Al,PN-Fe₃O₄-PEI and PN-Fe₃O₄-Bet）towards the sequestration of some typical pollutants in wastewater such as dyes（i.e.Methylene Blue（MB）,Congo red（CR）,Alizarin red（AR）,Acid chrome blue K（AK））,phosphates,heavy metals(i.e.copper ion,lead ion and hexavalent chromium（Cr（VI））and antibiotics（i.e.trimethoprim）were assessed via the batch mode.The surface nature and physicochemical properties of the formed adsorbents before and after the adsorption processes were assessed using analytical techniques such as X-ray photoelectron spectroscopy（XPS）,X-ray diffractometer（XRD）,Fourier transform infrared spectroscopy（FTIR）,scanning electron microscopy（SEM）,Bruaneur-Emmet-Teller（BET）method and the Vibrating Sample Magnetometer（VSM）.Results from these studies confirmed the formed adsorbents to be crystalline with mesoporous structure and superparamagnetic properties as well as the presence of some functional groups which play active roles in the adsorption processes.With the exception of the studies involving the uptake of Cu²⁺and Pb²⁺（which were assessed using the Atomic Absorption Spectroscopy）,the residual concentration of the pollutants after the adsorption processes were analyzed using the UV-vis spectrophotometer.The adsorption capacity was dependent on the solution p H and temperature of the pollutants and the maximum adsorption capacity of PN-Fe₃O₄-IDA from the Langmuir model was 43.5 mg g^–1 for MB（at 313 K）,0.90 mmol g^–1 for Cu²⁺and 0.36 mmol g^–1 for Pb²⁺,respectively（at 318K）.The fitting of adsorption isotherms to the experimental data showed that the uptake of MB and Pb²⁺onto PN-Fe₃O₄-IDA was well fitted by the Langmuir model whereas the Freundlich model best suited the uptake of Cu²⁺.These processes were observed to be significantly driven by the chemical forces as the pseudo-second kinetic order model and the Elovich equation best described the rate at which these pollutants were adsorbed.The results from the uptake of phosphate onto PN-Fe₃O₄-IDA-Fe demonstrated that the Freundlich isotherm model best fitted the experimental data with the maximum adsorption capacity observed to be 33.7 mg g^–1（mass as P）at 303 K.The kinetic adsorption process was observed to be better fitted by the pseudo-second-order kinetic model as compared to the pseudo-first-order kinetic model.The electrostatic attraction and ion exchange were observed to be the principal underlying mechanisms for the uptake of PO₄^3–onto PN-Fe₃O₄-IDA-Fe.Thermodynamic studies suggested that the adsorption process occurs via a chemical reaction（chemisorption）and is endothermic in nature.The efficiency of PN-Fe₃O₄-IDA-Zr for the removal of phosphates and alizarin red in solution was observed to be significantly dependent on some environmental factors such as p H,temperature and the presence of some common ions in solution.The maximum monolayer capacity of PN-Fe₃O₄-IDA-Zr in the absence of salts was 44.5 mg g^–1 for AR（T=303 K,p H=5.7）and 10.4 mg g^-1 for PO₄^3-（T=303 K,p H=3）.The Langmuir model and Freundlich model were observed to best fit the experimental data obtained for the uptake of AR and PO₄^3–onto PN-Fe₃O₄-IDA-Zr,respectively.The chemisorption process was noted to be the dominant reaction mechanism for both adsorption processes.In binary systems,PN-Fe₃O₄-IDA-Zr exhibited higher affinity for AR as compared to AK with the reason being ascribed to the difference in the interaction of Zr with the ortho-hydroxyl groups on these dyes.Adsorption studies indicated that PN-Fe₃O₄-IDA-Al had a maximum monolayer capacity of79.0 and 16.8 mg g^-1for CR and PO₄^3-,respectively.The Freundlich model was observed to better describe both adsorption processes with chemisorption being the principal underlying mechanism.Comparative studies showed that the removal efficiency of PN-Fe₃O₄-IDA-Al was comparable to some other reported adsorbents based on biomaterials for the remediation of wastewater.Results from using real water samples confirmed PN-Fe₃O₄-IDA-Al to be highly efficient for practical remediation processes.The efficiency of PN-Fe₃O₄-PEI as an adsorbent was investigated using Cr（VI）,PO₄^3–and CR as pollutants.Using the batch method,PN-Fe₃O₄-PEI exhibited a maximum monolayer adsorption capacity of 58.4,13.5 and 71.3 mg g^–1 for Cr（VI）,PO₄^3–and CR,respectively.Kinetic studies revealed that the Elovich equation,the pseudo-second-order kinetic model and double constant equation well fitted the experimental data for the uptake of Cr（VI）,PO₄^3–and CR onto PN-Fe₃O₄-PEI.These results may confirm the uptake of these pollutants to be mainly driven by chemical forces.In addition,PN-Fe₃O₄-PEI was observed to be efficient for the decontamination of the studied pollutants in real water samples as well as exhibit antibacterial properties towards the growth of S.aureus.Assessment of PN-Fe₃O₄-Bet for the sequestration of trimethoprim（TMP）from solution confirmed its efficiency for this purpose.The experimental adsorption capacity of 20.3 mg g^-1was recorded under optimum conditions(i.e.p H=4.3,m=1 g L^–1,C₀=50 mg L^–1,T=293 K).The chemisorption process was found to be the main mechanism for TMP adsorption onto MPN-Bet.Regeneration studies showed MPN-Bet loaded TMP was highly reusable after treatment with 0.1 mol L^–1 Na Cl solution.The assessment of the antibacterial properties of PN-Fe₃O₄-Bet indicated that PN-Fe₃O₄-Bet could effectively limit the growth of E.coli and S.aureus without causing damage to other living organisms（i.e.biocompatible）.Results from elucidating the influence of temperature on the adsorption process via thermodynamics study showed the adsorption process to be exothermic in nature.The facile synthetic route for these designed adsorbents which were performed under environmentally benign conditions coupled with other unique features of the adsorbents such as good removal efficiency towards the studied pollutants,high stability in solution,good regeneration properties and facile retrieval promote their potential for the treatment of real wastewater.The results from this study are expected to expound knowledge on the development of adsorbents based on agricultural waste materials with excellent features for the remediation of wastewater.