| Heavy metals in water pose a serious threat to water quality and ecological health owing to their high toxicity,cannot been degradation,and strong accumulation characteristics.Therefore,it is of great significance and urgency to develop advanced purification technology for the treatment of toxic metal-polluted water.Compared with conventional techniques such as chemical precipitation,membrane filtration and biological method,adsorption has been accepted as one of the most attractive techniques and widely applied as a result of its uncomplicated operation,excellent treatment effect,clean process and absent secondary pollution,etc.However,current adsorbents for water treatment are still difficult to meet the urgent demand for rapid,in-depth,and economic removal of heavy metals from water.The development of rapid and highly selective adsorption materials for heavy metal capture in water provides a feasible approach to overcome the current dilemma.(1)In view of the shortcomings of biochar(e.g.,the low adsorption capacity)and iron oxide nanoparticles(e.g.,uncomplete solid-liquid separation and difficult operation)when separately used,in this study we prepared a composite material(HFO-BC)through confining nano-sized ferric oxide within the pores of biochar using a "in situ deposition"technique.The hybrid adsorbents effectively combined the high activity and excellent hydraulic characteristic.The particle sizes of ferric oxide nanoparticles in HFO-BC are generally 20-50 nm,and its adsorption toward Cd(?)and Cu(?)increased with the elevated pH.The maximum adsorption capacities of Cd(?)and Cu(?)are 29.9 and 34.1 mg/g,respectively,with adsorption equilibrium time within 120 min.Moreover,HFOBC showed satisfactory anti-interference ability for Cd(?)and Cu(?)removal in water toward coexisting cations owing to the specific inner-sphere complexation between the immobilized HFO and targeted metals,for instance,when the molar concentration of coexisting ion Ca(?)was 50 times higher than the target metals,the adsorption capacities of Cd(?)and Cu(?)could still reach 5.8 and 6.0 mg/g.In addition,HFO-BC could effectively treat the simulated and real Cd(?)and Cu(?)-polluted electroplating wastewater by column adsorption,and the saturated adsorbent can be regenerated in situ.(2)Due to the geometric constraint of pore channel in biochar,the particle size distribution of nanoparticles in HFO-BC is very wide,which leads to the limited working adsorption capacity for heavy metal removal.Inspired by Derjaguin-Landau-Verwey-Overbeek(DLVO)theory,we fabricated a highly dispersed nano-sized ferric oxide through coating it into a charged biochar with high-density charged oxygen functional groups,which was obtained by HNO3 oxidization.The particle size of ferric oxide nanoparticles in the resultant composite(HFO-ABC)is ultrasmall,with the average particle size of 3.1 nm.The maximum adsorption capacities of HFOABC for Cd(?)and Cu(?)are 62.3 and 43.7 mg/g,respectively,which are much higher than that of HFO-BC.In addition to this,the experimental results of the pH effect,kinetics,competitive adsorption and column adsorption for HFO-ABC adsorption to the two metals are similar to those of HFO-BC.(3)Furthermore,taking Cd(?)as an example,the effect of immobilized charged functional groups covalently attached to biochar on the physicochemical properties and adsorption performance of the loaded ferric oxide nanoparticles was studied.The results showed that,with the increase of the charged group amount,the particle size of ferric oxide particles became smaller,and the dispersion became higher,as well as the adsorption capacity of Cd(?)increased.This is mainly because the nondiffusible charged groups on the surface of the carrier promote the dispersion of nanoparticles through enhancing the electrostatic repulsion of double electronic layer.Moreover,these groups can also drive permeation and pre-enrichment of target metal ions at the solid-liquid interface before adsorption through Donnan membrane effect,and thus improve the working adsorption capacity and removal of heavy metals in water.More importantly,the enhancement of functional groups on the activity of nanoparticles was not affected by pH,competitive ions and other factors.(4)Although the adsorption performance of ferric oxide nanoparticles was apparently improved by introducing the high-density charged groups,the adsorption time was still relatively long,i.e.,up to 120 min.To accelerate ionic pollutants adsorption onto HFObiochar hybrid adsorbents,KHCO3 was employed as pore expanding agent to prepare macro-mesoporous biochar as carrier,and a new composite adsorbent named HFO-LABC was obtained.The results show that the adsorption of Cd(?)and Cu(?)by HFO-LABC not only has the same excellent properties as the former two materials,but also greatly reduces the proportion of micropores in LABC compared with BC and ABC,thus significantly increases the adsorption speed of heavy metals.Under the similar conditions,the adsorption equilibrium time of Cd(?)and Cu(?)on HFO-LABC was only 10 min,which was 1/12 of that of HFO-BC and HFO-ABC.In this study,a category of high-performance composite functional nanomaterials were prepared and basically realized the rapid and efficient removal of heavy metals in water.Moreover,the exhausted composites could be effectively regenerated using acidsalt solution and further achieve reusability.This study is expected to provide an important reference for the development of advanced treatment technology for heavy metals in water,and also provide theoretical basis and method guide for the development and application of similar composite environmental functional water treatment materials.Figure 59 Table 17 Reference 187... |
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