農(nóng)林生物質(zhì)制備鐵炭復合材料及其環(huán)境污染治理應用的研究進展

邱 凌，周勤勤，朱銘強，郭曉慧，范瓊波

農(nóng)林生物質(zhì)制備鐵炭復合材料及其環(huán)境污染治理應用的研究進展

邱 凌，周勤勤，朱銘強※，郭曉慧，范瓊波

（1. 西北農(nóng)林科技大學機械與電子工程學院，楊凌 712100；2. 農(nóng)業(yè)農(nóng)村部農(nóng)村可再生能源開發(fā)利用西部科學觀測實驗站，楊凌 712100）

以農(nóng)林生物質(zhì)為原材料，通過加入鐵磁性助劑制備鐵炭復合材料是農(nóng)林生物質(zhì)高值化利用和受污染水體及土壤治理的重要途徑。鐵炭復合材料具有高比表面積、豐富表面官能團和優(yōu)異吸附性能，能夠通過表面物理吸附和氧化還原作用，快速吸附污水中的重金屬離子，并在外部磁場的吸引下實現(xiàn)快速分離回收和循環(huán)使用。該研究論述了不同制備方法的鐵炭復合材料及其材料性能，對其去除有機染料污染物、治理污水和土壤重金屬的研究現(xiàn)狀及發(fā)展動態(tài)進行了分析和討論。在此基礎上，結合鐵炭復合材料的結構發(fā)育機理和污水治理及土壤改良的產(chǎn)業(yè)發(fā)展現(xiàn)狀，提出了兼顧低成本、易合成、高效益的復合材料制備方式建議，以期為其在環(huán)境污染治理中的廣泛應用提供理論和實踐參考，進而推動農(nóng)林生物質(zhì)資源化高值利用，助力生態(tài)環(huán)境的綠色低碳高質(zhì)量發(fā)展。

生物質(zhì)；重金屬；污染；鐵炭復合材料

0 引 言

環(huán)境污染主要與城市化和工業(yè)化進程中排放的有機污染物及重金屬有關[1]，特別是染料、藥品、農(nóng)藥等有機分子和重金屬離子等化學物質(zhì)具有極強的穩(wěn)定性[2]，此類物質(zhì)積累對環(huán)境及水生生物具有很大的危害性[3]，目前30%的工業(yè)污水未經(jīng)處理最終進入湖泊和河流，嚴重危及人類生存環(huán)境和安全用水[4]。近年來，利用農(nóng)林生物質(zhì)制備鐵炭復合材料成為研究的熱點，其在環(huán)境污染治理中具有廣闊的應用前景[5]，目前研究主要聚焦于通過研究和調(diào)控高比表面積活性炭（Activated Carbon，AC）材料的制備條件及其方法，探索其微孔和中孔形成機理及其吸附特性等[6]。利用農(nóng)林生物質(zhì)制備的活性炭通常具有較高的比表面積、發(fā)達的孔隙率和豐富的表面官能團，可作為一種高性能吸附劑[7]。然而，粉末狀活性炭在處理過的污水介質(zhì)中的后續(xù)分離過程，通常需要通過離心或過濾來實現(xiàn)，制約了其規(guī)?；瘧肹8]。因此，通過將鐵磁性助劑及其氧化物介導進活性炭基質(zhì)中制備鐵炭復合材料[9]，利用其鐵磁性的特點，能夠快速將鐵炭復合材料從污水介質(zhì)中回收，從而可以有效解決制約活性炭材料在環(huán)境污染治理中循環(huán)利用的技術瓶頸，推進農(nóng)林生物質(zhì)資源高值化利用。

1 制備鐵炭復合材料的原料和助劑特性

1.1 制備鐵炭復合材料的農(nóng)林生物質(zhì)特性

生物質(zhì)通常指農(nóng)林廢棄物，主要包括畜禽糞便、農(nóng)作物秸稈、城鄉(xiāng)有機垃圾、農(nóng)業(yè)加工殘余物、林業(yè)及林產(chǎn)加工剩余物等。農(nóng)林生物質(zhì)作為一種有機含碳物質(zhì)，通常由纖維素、半纖維素、木質(zhì)素、灰分、粗蛋白及少量的無機礦物質(zhì)組成（表1）。其中，纖維素、半纖維素、木質(zhì)素是植物細胞壁的主要組分，約占木質(zhì)纖維素總質(zhì)量的90%[10]。農(nóng)林生物質(zhì)各組分之間相互穿插交織，構成復雜的高聚合物體系（圖1），是自然界中產(chǎn)量最大的可持續(xù)碳資源。

據(jù)統(tǒng)計，中國每年產(chǎn)生1 500億m3農(nóng)林生物質(zhì)，其中，畜禽糞便占50%，秸稈占40%，有機垃圾占6%，農(nóng)業(yè)品加工殘余物占4%；每年森林采伐量約2.5億m3，可產(chǎn)生采伐、造材等林業(yè)剩余物1.1億t[11]。以農(nóng)林生物質(zhì)為原料，采用先進的轉化技術制備的鐵炭復合材料，具有含碳量高、穩(wěn)定性強、孔隙豐富、比表面積大（10～103m2/g）、吸附能力強、耐降解性高、表面帶有含氧官能團和負電荷等優(yōu)點[12]，可廣泛應用于治理污水和土壤重金屬環(huán)境污染。

表1 農(nóng)林生物質(zhì)成分分析

1.2 制備鐵炭復合材料的磁性助劑特性

在制備鐵炭復合材料的磁性助劑中，由于Fe元素獲取方便、價格低廉、安全無毒，故應用最為廣泛。常用的鐵磁性助劑包括FeCl3·6H2O、FeSO4·7H2O、Fe(NO3)3·9H2O和FeCl2·4H2O等金屬鹽。Rodriguez-Sanches等[13]通過將板栗殼在FeCl3中浸漬處理后制備得到鐵炭復合材料，用于工業(yè)廢水處理，結果表明，其對廢水中Hg0的去除量為63.62g/g，可有效去除工業(yè)過程中Hg0的排放。

活性炭是制備鐵炭復合材料的優(yōu)質(zhì)多孔吸附載體，其顆粒大小對吸附效果具有重要影響[14]。雖然大顆粒有利于液固分離，但低比重和大顆粒的包裹限制了活性炭的吸附動力學和吸附容量；小顆粒不僅可以增加吸附劑的容量，并能實現(xiàn)快速平衡[15]。傳統(tǒng)的分離方法難以實現(xiàn)小顆?；蚍勰罨钚蕴吭趶U水污染治理中的固液分離，限制了其在循環(huán)吸附中的大量應用。因此，通過將不同的磁性助劑與活性炭耦合制備鐵炭復合材料的工藝和技術，成為農(nóng)林生物質(zhì)資源化利用和廢水污染治理的研究熱點（表2）。

圖1 植物細胞壁結構示意圖

表2 不同原料和磁性助劑制備鐵炭復合材料的反應條件

Costa等[21]用3.0 g Fe(NO3)3·9H2O對20 g大豆皮進行浸漬處理后，采用一步熱解法在管式爐中以10 ℃/min的升溫速率，在N2氛圍下升溫至550 ℃熱解2 h制備出鐵炭復合材料（CM1.3–800），用于廢水中酚類化合物的吸附特性研究，結果表明，鐵炭復合材料（CM1.3–800）的飽和磁化強度為107 A/m，對咖啡酸的吸附量可達418 mg/g，可有效去除咖啡加工廢水中的有機物。在磁分離過程中，具有一定的飽和磁化率，使其在外加磁場的作用下，能夠快速分離。

Qu等[26]用FeCl3?6H2O對水葫蘆進行了浸漬處理，通過水熱反應，制備得到鐵炭復合材料（MPBCMW3），其比表面積高達2 097.51 m2/g，對六價鉻（Cr（VI））和四環(huán)素（TC）最大吸附量分別為202.61和202.62 mg/g；經(jīng)過3次循環(huán)吸附后，MPBCMW3對Cr（VI）和TC的脫附率超過83.42%和90.91%，吸附量只下降了11.75%和22.03%，表明MPBCMW3具有良好的可重復使用性。由此可知，農(nóng)林生物質(zhì)加入磁性助劑制備為鐵炭復合材料后，利用磁分離技術，能夠快捷、高效、低成本的分離回收復合材料，進而實現(xiàn)其循環(huán)使用。

2 農(nóng)林生物質(zhì)制備鐵炭復合材料研究進展

2.1 水熱合成法制備鐵炭復合材料研究進展

將農(nóng)林生物質(zhì)和水在180～350 ℃、1 MPa～1 GPa的高壓釜中，通過熱化學反應即可合成化學物質(zhì)[27]。水熱反應形成的微環(huán)境可加速生物質(zhì)與溶液之間的理化作用，促進離子與酸/堿的反應，降解木質(zhì)纖維素細胞壁中的碳水化合物，保留原有碳骨架，進而形成多孔結構的復合碳骨架材料[28]。Prasannamedha等[24]以甘蔗渣為原料，采用兩步水熱炭化法，在Fe(NO3)3·9H2O的作用下制備鐵炭復合材料。檢測表明，所制備的鐵炭復合材料存在Fe/Fe3C/γ-Fe2O3，磁化效果為32.84 A/m，對磺胺甲惡唑的最大吸附量為169.49 mg/g。Wu等[29]用廢紙箱的木質(zhì)纖維素與FeCl3·6H2O進行兩步水熱處理，在高壓反應釜中溫度200 ℃反應10 h制備鐵炭復合材料。吸附試驗發(fā)現(xiàn)，在pH值為2的酸性條件下，對藍色染料（DB 56）和黃色染料（RY 3）的去除率分別達到81.53%和96.77%，且經(jīng)過5次循環(huán)吸附后，去除率仍達到70%以上。Cai等[30]以花生殼為原料，在FeCl3·6H2O和六亞甲基二胺的作用下，采用一步水熱法，成功制備了對Cr（VI）具有良好吸附性能的氨基功能化鐵炭復合材料，其吸附量為142.86 mg/g，可循環(huán)吸附3次。王森等[31]對水熱過程中原料種類、反應溫度、停留時間、催化劑和溶液的循環(huán)利用時間等因素進行了研究，表明水熱反應條件對水熱炭化過程和最終炭化產(chǎn)物的結構及性質(zhì)產(chǎn)生較大影響，水介質(zhì)氛圍有助于炭化材料表面含氧官能團的形成，因此，水熱炭化產(chǎn)物含有豐富的表面官能團。

由此可見，通過兩步和一步水熱炭化法可以將金屬鹽通過浸漬傳導到農(nóng)林生物質(zhì)的表面或內(nèi)部，通過炭化制備出表面官能團豐富、多孔結構、能夠低成本分離回收的鐵炭復合材料，有效解決環(huán)境污染治理技術瓶頸，助力生態(tài)環(huán)境高質(zhì)量發(fā)展。

2.2 溶劑熱法制備鐵炭復合材料研究進展

將水熱法中的水溶液換成有機溶劑或非水溶媒（例如：有機胺、醇、氨、四氯化碳或苯等），通過金屬鹽的水解作用，生成金屬氧化物晶粒負載到生物炭上。該法能較好的控制磁性晶粒在活性炭表面的生長，從而提供更多的吸附位點，使鐵炭復合材料具有更好的吸附性能[32]。Fei等[33]利用氧化石墨烯（GO）和Fe3+做原料，采用一鍋溶劑熱法制備鐵炭復合材料，并測定其對亞甲基藍（Methylene Blue，MB）的吸附性能，研究表明，用鐵炭復合材料吸附30 min后，其對MB的吸附量可達9.73 mg/g，且經(jīng)過5次循環(huán)重復使用后，對MB的吸附量仍大于5.79 mg/g。由此可見，采用該法制備的鐵炭復合材料，具有優(yōu)良的可重復使用和較強的吸附去除MB的性能。

溶劑熱法除了采用生物炭做載體外，還可將磁性助劑介導入農(nóng)林生物質(zhì)，進行耦合反應，以達到提質(zhì)增效的目的。Wang等[34]將磁性助劑MnFe2O4直接加入椰殼中，通過一步溶劑熱法，成功制備了鐵炭復合材料（MnFe2O4@AC），在25 ℃條件下，0.2 g吸附劑的吸附量約為226 mg/g，表明鐵炭復合材料（MnFe2O4@AC）具有吸附量大、磁性強的優(yōu)點，對乙草胺等有機污染物的吸附、分離、降解等方面具有良好的應用前景。Ren等[35]以Fe(NO3)3和環(huán)糊精為原料，尿素為堿源，通過一步溶劑熱法，合成了比表面積為112.91 m2/g的磁性納米吸附劑（Fe3O4@C）。研究表明，磁性納米吸附劑（Fe3O4@C）對六價鉻（Cr（VI））和剛果紅（CR）的最大吸附量分別為33.35和262.72 mg/g，具備較強的去除能力。

由此可見，與其他制備方法相比，溶劑熱合成工藝和技術的顯著特點在于能夠有效抑制產(chǎn)物的氧化[36]，防止空氣中氧的污染，對制備高品質(zhì)鐵炭復合材料表現(xiàn)出非常顯著的優(yōu)勢。

2.3 浸漬熱解法制備鐵炭復合材料研究進展

將農(nóng)林生物質(zhì)在含過渡金屬鹽的溶液中浸漬處理后，對熱穩(wěn)定性不同、能形成相分離結構的聚合物進行炭化，熱穩(wěn)定性高的聚合物（炭前驅體聚合物）經(jīng)過高溫炭化形成炭基體，熱穩(wěn)定性低的聚合物（造孔劑）經(jīng)熱解揮發(fā)后，在炭基體中留下大量的孔隙，進而可得到高品位的鐵炭復合材料[37]。Zhu等[38]以黑液木質(zhì)素和污泥為原料，以KOH為活化劑，采用一步熱解制備出磁性活性炭（Magnetic activated carbon，MAC）。經(jīng)過5次吸附/解吸后，MAC的回收率均大于84.0%，表明MAC具有良好的再生能力。Ahmed等[39]以微孔三嗪類聚合物（COP）為原料，浸漬Zn(OH)2后，在N2氛圍中，以1 000 ℃熱解制得新型炭材料。負載Zn(OH)2后，由于中孔體積的增加，使碳的比表面積和總孔體積增大，其對磺胺甲惡唑和磺胺氯吡啶的最大吸附量分別達到514和430 mg/g，在經(jīng)過4次吸附/解析后，吸附容量仍保持95%。上述結果分析表明，用聚合物浸漬熱解法制備的磁性吸附劑，具有優(yōu)異的吸附凈化能力，能夠有效去除污水中殘留的污染物。

2.4 化學共沉淀法制備鐵炭復合材料研究進展

在沉淀劑及配位劑作用下，含有2種或多種陽離子的金屬鹽溶液生成難溶性的鹽或氧化物，均一地沉積到活性炭上，再經(jīng)過烘干或者煅燒處理進而制備出鐵炭復合材料[40]。Feng 等[41]將金屬鹽FeCl3·6H2O和FeSO4·7H2O加入到木基活性炭中，采用化學共沉淀法制備鐵炭復合材料用于處理造紙污水的吸附，其最大飽和磁化強度可達29.68 A/m，在pH值為2時，對化學需氧量（Chemical Oxygen Demand，COD）的去除可達65 mg/g。

共沉淀法與吸附法的區(qū)別在于共沉淀法直接將活性炭與金屬鹽溶液混合，將金屬離子和金屬氧化物先吸附在表面或者進入孔道內(nèi)部，再原位沉淀實現(xiàn)負載的目的。Gao等[42]以黑木耳廢渣為原料，采用化學共沉淀法和浸漬-熱解法制備了2種類型的鐵炭復合材料（MBC-1和MBC-2）用于污水中四環(huán)素（TC）的去除，結果表明，化學共沉淀法制備的鐵炭復合材料MBC-1對污水中TC的去除量達到42.31 mg/g，比浸漬-熱解法制備的鐵炭復合材料MBC-2對TC的去除量24.31 mg/g提高了1.74倍，表現(xiàn)出了更高的吸附能力。由此可知，以化學共沉淀法得到的鐵炭復合材料，磁性相對固定且穩(wěn)定，過程相對簡單。

2.5 電弧放電法制備鐵炭復合材料研究進展

用較粗的石墨棒為陰極，較細石墨棒為陽極，在真空反應室中充入氦氣、氬氣等惰性氣體，在電弧放電過程中，碳原子和填充在陽極石墨棒內(nèi)的金屬催化劑蒸發(fā)，碳原子在多重因素的作用下重組形成碳納米材料，同時在石墨陰極上沉積出產(chǎn)物[43]。Hu等[44]采用一步法直流電弧放電，在不同的氣體壓力下，將不同摩爾比的NH3加入到He/CH4氣體混合物中，合成了具有高濃度氨基功能化的石墨包覆磁性納米顆粒。

Jagannatham等[45]采用旋轉陰極電弧放電法在自然環(huán)境下合成了碳納米管，在不同的沉積時間對CNTs進行化學鍍鎳，發(fā)現(xiàn)化學沉積鎳的量隨沉積時間的增加而增加，且隨著沉積時間的延長，金屬離子還原增強，當沉積時間為60 min時，可獲得均勻的Ni涂層。Hu等[46]通過調(diào)整電弧等離子體的合成參數(shù)，對封裝石墨殼的表面形貌和質(zhì)量進行了系統(tǒng)研究，發(fā)現(xiàn)當CH4的濃度從0增加到50%時，涂層石墨殼的最外層趨于光滑和清潔，通過距圓心1～10 cm的收集距離，可獲得石墨化程度較高的表面形貌；當工作氣體壓力從13 332 Pa降低到3 333 Pa時，最外層的碳納米環(huán)在徑向尺度上呈膨脹演化，甚至出現(xiàn)連續(xù)的非晶態(tài)覆蓋層。

由此可見，電弧放電法的優(yōu)勢在于能夠通過調(diào)整電極電勢與電流密度來精確控制納米顆粒的合成，為表面形貌和性能可調(diào)的鐵炭復合材料的制備提供新思路和途徑。

2.6 微波法制備鐵炭復合材料研究進展

微波加熱電磁波與制備材料的分子以更均勻的方式相互作用，有助于在材料內(nèi)部均勻和更快地傳遞能量，從而實現(xiàn)節(jié)約能源，提高效益的目的。Salem等[47]采用微波輔助修飾氧化鐵納米顆粒的方法，將杏仁殼和核桃殼粉末復合浸漬，研究了ZnCl2、FeCl3和FeCl2混合物對陽離子染料吸附效率的影響，發(fā)現(xiàn)在中性條件下，F(xiàn)eCl3浸漬所得的鐵炭復合材料對陽離子染料的最大吸附量為130 mg/g，且在動態(tài)吸附體系中可提供約1 000 m2/g的比表面積。Yang 等[48]以稻稈為原料，利用微波和蒸汽活化技術制備了一種磁性鈷鐵多孔炭，用于去除燃煤煙氣中的單質(zhì)汞。結果表明，鈷氧化物和鐵氧化物是除汞的主要活性成分，制備的鈷-鐵炭復合材料中的Co3+/ Co2+和Fe3+/ Fe2+參與了Hg0的捕獲過程，對Hg0的最大吸附量為60.14g/g，同時鈷-鐵炭復合材料多孔碳具有良好的再生性能，經(jīng)過6次重復吸附之后，其對Hg0的去除率仍可達到60.12%。

3 鐵炭復合材料治理環(huán)境污染研究進展

農(nóng)林生物質(zhì)通過水熱合成法等不同的技術制備出的鐵炭復合材料，不僅具有豐富的孔隙結構和含氧官能團，同時是一種具有高密度吸附位點的吸附劑，展現(xiàn)出優(yōu)良的環(huán)境污染治理能力，在環(huán)境污染治理中具有非常廣闊的應用前景，圖2展示了用不同農(nóng)林生物質(zhì)和磁性助劑制備的鐵炭復合材料在去除有機染料污染、治理污水和土壤重金屬中的綜合應用示意。

圖2 鐵炭復合材料在環(huán)境污染治理中的綜合應用

3.1 鐵炭復合材料治理染料污水污染研究進展

中國每年產(chǎn)生染料污水約40億t，位列全國工業(yè)排放污水第五[49]。由于染料污水色度深、有機污染物含量高、難生物降解，尤其是印染廢水存在著對人類健康和海洋生物具有致癌和誘變作用的芳香環(huán)[50]，已成為污水治理的研究重點，目前大量的研究聚集于通過吸附[51]、絮凝[52]、光催化降解[53]和膜過濾[54]等技術，去除染料污水中的有害因子的探索。

膜過濾技術能耗低，處理過程容易控制，可對印染污水進行深度處理，但存在著潛在的膜污染風險，增加了后續(xù)處理的難度[55]。光催化降解技術在經(jīng)濟上可行，但會導致不完全降解[56]?；钚蕴课郊夹g工藝簡單，成本低且環(huán)保，滿足環(huán)境綠色可持續(xù)發(fā)展，是目前治理印染廢水污染的通用技術。

Foroutan等[57]以海藻為原料，與Fe3O4納米顆粒進行復合，制備了一種可循環(huán)利用的高效鐵炭復合材料，對印染廢水中的亞甲基藍（MB）和甲基紫（MV）進行吸附特性及機理研究。結果表明，其飽和磁化強度為26.57 A/m，比表面積（BET）為126.77 m2/g，對亞甲基藍（MB）和甲基紫（MV）的最大吸附量分別達到60.60和59.88 mg/g。經(jīng)過7次重復使用后，該鐵炭復合材料對印染廢水中亞甲基藍（MB）和甲基紫（MV）染料的多次回收處理效果良好，且不顯著降低其對印染物的去除率，由此可見，鐵炭復合材料在印染廢水凈化方面具有廣闊的應用前景。

由于鐵炭復合材料具有較高的比表面積和發(fā)達的孔隙結構及豐富的表面化學官能團，對印染廢水中的亞甲基藍（MB）、甲基紫（MV）、剛果紅（CR）、甲基橙（MO）、孔雀石綠（MG）和結晶紫（CV）等污染成分具有良好的去除效果（表3）。通常情況下，鐵炭復合材料對染料污染成分的去除是通過物理吸附與化學吸附的協(xié)調(diào)作用完成的，具有極強的選擇性，其脫色能力依次為堿性染料、直接染料、酸性染料和硫化染料。這主要是鐵炭復合材料的具有豐富的介孔和微孔，親水性強，能快速實現(xiàn)吸附脫色過程[58]。因此，制備高品質(zhì)的鐵炭復合材料對治理印染廢水污染具有重要意義。

表3 鐵炭復合材料對印染污水污染成分的去除效果

3.2 鐵炭復合材料去除污水重金屬研究進展

鉻、汞、鎘、鉛、砷、銅、鎳等重金屬離子進入人體后，與體內(nèi)高分子物質(zhì)（如蛋白質(zhì)等）發(fā)生反應從而使其失去活性，在人體器官中逐漸積累，造成慢性中毒，嚴重威脅人類健康。重金屬吸附機理涉及多種機理的結合，因前驅體材料和重金屬的不同類型而異。鐵炭復合材料對重金屬的物理吸附是由活性炭表面分子與重金屬離子之間發(fā)生的范德華力引起的[69]，其中重金屬在較高的價態(tài)下攜帶更多的電荷，從而產(chǎn)生更強的靜電相互作用和吸附能力，通過氧化還原反應，改變元素的存在形態(tài)，特別是價態(tài)變化影響元素化學行為、生物有效性和重金屬的遷移能力[70]。

Fang等[71]通過高強度研磨對椰殼進行預處理后，制備出活性炭（HAC），在酸堿溶液洗滌的含鉻HAC上建立了2種鉻離子去除機理，包括六價鉻（Cr（VI））還原為三價鉻（Cr（III）），鉻酸根（CrO42-）與羧基（COOH）表面官能團氫鍵結合，隨后在HAC表面和孔隙內(nèi)析出氫氧化鉻（Cr（OH）3），證實了Cr（VI）在HAC表面的吸附是多層吸附和化學吸附的綜合結果。

鐵炭復合材料因其比表面高、孔徑結構豐富，分離方便、成本低等優(yōu)點，被廣泛應用于去除污水重金屬的研究（表4）。由表4可見，不同原料及方法制備的鐵炭復合材料對水污染中鉛、汞、鎘、鉻、鎳、鋅、銅等重金屬均表現(xiàn)出較好的去除效果，表明鐵炭復合材料在去除污水中重金屬方面具有優(yōu)良的應用價值。

Zhang等[72]研究了在不同熱解溫度下，水熱法制備的油菜秸稈鐵炭復合材料對污水中Pb（II）和Cd（II）的去除特性和機理，結果表明，油菜秸稈鐵炭復合材料對Pb（II）和Cd（II）的最大吸附量分別為253.2和73.3 mg/g，通過熱力學分析，表明其吸附Pb（II）和Cd（II）是自發(fā)的吸熱反應，且主要取決于材料表面不均勻的活性位點。

表4 鐵炭復合材料去除污水中重金屬的效果

3.3 鐵炭復合材料治理土壤重金屬污染研究進展

鐵炭復合材料因其具有致密的微孔結構和巨大的比表面積，對鉛、汞、鉻、鎘等重金屬表現(xiàn)出較強的吸附能力，同時因其制備生產(chǎn)成本低、生態(tài)安全、無污染、可大面積推廣等顯著特點，成為一種高效、廉價的土壤重金屬修復劑。李鴻博等[80]研究發(fā)現(xiàn)，通過鐵炭復合材料的物理吸附、靜電吸附、離子交換、絡合、沉淀和氧化還原等作用，可以直接吸附重金屬離子。閆翠俠等[81]用雞糞為原料制備鐵炭復合材料，對土壤中Cd、Pb進行了修復，結果表明，添加雞糞鐵炭復合材料，能顯著提高土壤pH值（<0.05），對土壤 Pb、Cd最大吸附量分別達到52.02（BC600）和242.59 mg/g（BC800），表現(xiàn)出較強的鈍化作用和效果。

鐵炭復合材料作為土壤重金屬鈍化劑的有效性取決于原料類型、熱解條件、改性材料性質(zhì)等物理化學特性，以及土壤環(huán)境條件、化學形態(tài)和金屬離子濃度。鐵炭復合材料用于修復土壤時，通過其氧化物、氫氧化物和碳酸鹽和土壤元素的反應，改變土壤的理化特性，固定土壤金屬離子，提高土壤質(zhì)量和生產(chǎn)力。除此之外，鐵炭復合材料在土壤系統(tǒng)中具有多種作用，如調(diào)節(jié)土壤pH值、氧化還原電位及釋放還原離子等，進而固定并降低土壤重金屬的生物利用度和危害，提高酸性土壤的pH值和養(yǎng)分，改變土壤微生物群落結構，改善土壤性質(zhì)，提高土壤持水保肥能力，促進農(nóng)作物持續(xù)健康生長（表5）。Xu等[82]以水稻秸稈為原材料制備鐵炭復合材料，用于修復土壤重金屬和提高土壤微生物豐富度和多樣性研究，結果表明，水稻秸稈鐵炭復合材料有效固定了土壤重金屬，降低了土壤鐵的生物有效性，提高了土壤錳的生物有效性，從而潛在地影響了土壤微量養(yǎng)分的肥力和土地生產(chǎn)能力。

表5 鐵炭復合材料對土壤重金屬的修復效果

4 結論與展望

利用農(nóng)林生物質(zhì)與磁性助劑反應制備的鐵炭復合材料，具有孔隙結構發(fā)達、比表面積高、表面官能團豐富的優(yōu)點。通過分析可知，水熱合成法有助于炭化材料表面含氧官能團的形成；溶劑熱法能夠有效地抑制產(chǎn)物的氧化，有利于高品位鐵炭復合材料的制備；浸漬熱解法可在炭活化產(chǎn)物中生成大量的孔隙結構；化學共沉淀法可將金屬離子和金屬氧化物附著在炭材料表面或者孔道內(nèi)部；電弧放電法可通過調(diào)整電極電勢與電流密度精確控制納米顆粒的合成；微波法可實現(xiàn)內(nèi)部加熱，縮短鐵炭復合材料合成時間。鐵炭復合材料致密的微孔結構和發(fā)達的比表面積，通過范德華力的物理吸附和氧化還原反應，對鉛、汞、鎘等重金屬離子具有較強的吸附和固定能力，也可有效去除污水中的染料污染物。因此，鐵炭復合材料在去除有機染料污染、治理污水和土壤重金屬吸附等領域的應用，可助力生態(tài)環(huán)境綠色低碳高質(zhì)量發(fā)展。

鐵炭復合材料不僅可以有效吸附各類污染物和重金屬，而且能夠通過快速固液分離，達到重復利用的目的。雖然目前的研究豐富了鐵炭復合材料的制備技術和應用，但仍需進一步研究和探索以下科學和技術問題：

1）不同的制備工藝和參數(shù)對鐵炭復合材料微觀結構和性能的影響特性；

2）鐵炭復合材料的孔徑結構形成機理與吸附性能之間的耦合關系；

3）污染物釋放和回收難題導致的二次污染的長效檢測和治理機制；

4）鐵炭復合材料用于環(huán)境污染治理的技術經(jīng)濟綜合評價。

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Research progress on the preparation of iron-carbon composites from agricultural and forestry biomass and their application in improving environmental pollution

Qiu Ling, Zhou Qinqin, Zhu Mingqiang※, Guo Xiaohui, Fan Qiongbo

(1.,,,712100,; 2...,,712100,)

An ever-increasing number of pollutants have posed serious hazards to human health and ecological environment, especially industrial wastewater, dye wastewater, and heavy-metal carcinogenic substances with the development of industrialization and urbanization in recent years. Fortunately, the iron-carbon composites can be expected to prepare using agricultural and forestry wastes. Among them, ferromagnetic additives have been widely used in the treatment of environmental pollution, due to the high specific surface area, better porosity, and abundant surface functional groups. The current preparation of iron-carbon composites includes hydrothermal synthesis, solvent heat, chemical co-precipitation, arc discharge, impregnation pyrolysis, and microwave. In this review, the latest research progress was summarized for the pros and cons of various syntheses. Among them, the hydrothermal environment accelerated the physicochemical interaction between the biomass and the aqueous solution in the hydrothermal synthesis. In turn, the formation of oxygen-containing functional groups was promoted on the surface of the carbonized materials. The solvent heat method was utilized to effectively inhibit the oxidation of products for the preparation of high-purity substances. The impregnation pyrolysis greatly contributed to a large number of pore structures in the carbonized products. The chemical co-precipitation was able to attach the metal ions and metal oxides to the surface of carbon materials or inside the pore channels. The arc discharge was used to precisely control the synthesis of nanoparticles via the varying electrode potential and current density. The microwave method was applied to realize the internal heating for less reaction time. The prepared iron-carbon composites exhibited excellent adsorption performance, easy separation, and high recycling rate. Extensive application prospects can be expected in the potential treatment of pollutants. A systematic investigation was then focused on the application progress of iron-carbon composites prepared from agricultural and forestry wastes in environmental pollution management, especially, the removal of heavy metals (Zn, Pb, Cd, Cr, Co, Ca, Mg, and Ni) from the wastewater, the treatment of dye wastewater, and the soil heavy metal pollution. More importantly, the removal of heavy metals and dyeing wastewater contained a combination of multiple adsorptions. Among them, the physical adsorption was caused by the Van der Waals forces between the molecules on the surface of iron-carbon composites and heavy metal or dye pollutant ions. The chemisorption was the process in the presence of elements via the redox reactions, especially the change of valence state. The optimal adsorption was achieved under the various chemical behavior, biological effectiveness, and migration ability of heavy metals. As such, the heavy metals were remediated in the soil pollutants, due to the significant effect of the iron-carbon composites on the immobilization of metal ions in the soil. Specifically, the iron-carbon composites with positive surfaces shared a great ability to immobilize anionic pollutants, whereas, the iron-carbon composites with negative surfaces mainly immobilized the cationic pollutants. The modified biochar can be expected to serve as a very promising immobilizer for soil heavy metal pollution. Therefore, the iron-carbon composites were prepared from the agricultural and forestry wastes in the environmental pollution remediation applications. Therefore, the low-cost, high-performance, high-efficiency adsorbent and remediation agent can provide great potential to leading technology and material for future environmental pollution treatment.

biomass; heavy metals; contaminant; iron-carbon composites

10.11975/j.issn.1002-6819.2022.22.019

S216.2

A

1002-6819(2022)-22-0172-11

邱凌，周勤勤，朱銘強，等. 農(nóng)林生物質(zhì)制備鐵炭復合材料及其環(huán)境污染治理應用的研究進展[J]. 農(nóng)業(yè)工程學報，2022，38(22)：172-182.doi：10.11975/j.issn.1002-6819.2022.22.019 http://www.tcsae.org

Qiu Ling, Zhou Qinqin, Zhu Mingqiang, et al. Research progress on the preparation of iron-carbon composites from agricultural and forestry biomass and their application in improving environmental pollution[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2022, 38(22): 172-182. (in Chinese with English abstract) doi：10.11975/j.issn.1002-6819.2022.22.019 http://www.tcsae.org

2022-08-09

2022-11-11

陜西省農(nóng)業(yè)科技創(chuàng)新驅動項目（NYKJ-2022-YL(XN)17）：黃河流域農(nóng)業(yè)面源污染防控技術研發(fā)與示范；國家自然科學基金青年項目（31900105）：磁性鐵炭復合材料基材料對厭氧消化微生物種間電子傳遞的促進效應機制研究

邱凌，教授，博士生導師，研究方向為生物質(zhì)能源與綠色低碳農(nóng)業(yè)工程技術教學與研究。Email：3037296930@qq.com

朱銘強，教授，博士生導師，研究方向為生物質(zhì)能源與綠色低碳農(nóng)業(yè)工程技術研究。Email：zmqsx@nwsuaf.edu.cn