王 月 ,熊振湖 *,周建國(guó) (.天津城市建設(shè)學(xué)院環(huán)境與市政工程系,天津市水質(zhì)科學(xué)與技術(shù)重點(diǎn)實(shí)驗(yàn)室,天津300384；.天津城市建設(shè)學(xué)院材料科學(xué)與工程系,天津 300384)

杯[4]芳烴修飾Amberlite XAD-4樹(shù)脂去除水中雙氯芬酸

王 月1,熊振湖1*,周建國(guó)2(1.天津城市建設(shè)學(xué)院環(huán)境與市政工程系,天津市水質(zhì)科學(xué)與技術(shù)重點(diǎn)實(shí)驗(yàn)室,天津300384；2.天津城市建設(shè)學(xué)院材料科學(xué)與工程系,天津 300384)

通過(guò)偶氮化反應(yīng)將合成的去叔丁基杯[4]芳烴連接到Amberlite XAD-4樹(shù)脂上,并且采用FTIR、SEM和TG/DTA法表征了杯[4]芳烴修飾Amberlite XAD-4樹(shù)脂的結(jié)構(gòu).結(jié)果表明,水溶液中杯[4]芳烴修飾Amberlite XAD-4樹(shù)脂對(duì)雙氯芬酸的去除率遠(yuǎn)大于單獨(dú)Amberlite XAD-4樹(shù)脂和杯[4]芳烴.雙氯芬酸的濃度為20mg/L時(shí),隨著杯[4]芳烴修飾AmberliteXAD-4樹(shù)脂投加量的增加,雙氯芬酸的去除率增加很快.當(dāng)吸附劑量增加到80mg/L時(shí),雙氯芬酸的去除率為92.8%,并且達(dá)到吸附平衡,吸附的雙氯芬酸量為34.02mg/g. Langmuir和Freundlich等溫線與實(shí)驗(yàn)數(shù)據(jù)均有很好的擬合度.對(duì)熱力學(xué)參數(shù)的計(jì)算表明,△H與△G負(fù)值顯示出反應(yīng)的放熱和自發(fā)過(guò)程.

杯[4]芳烴；AmberliteXAD-4樹(shù)脂；修飾；雙氯芬酸；吸附

雙氯芬酸(DCF)是一種具有鎮(zhèn)痛、抗關(guān)節(jié)炎和抗風(fēng)濕作用的非甾體抗炎藥,人類(lèi)服用 DCF之后有15%以原藥的形式排出體外[1].由于DCF生物降解能力低和在環(huán)境中的持久性,污水處理廠僅能將其部分去除(50%),在污水處理廠出水中的濃度已達(dá)到0.14～1.48μg/L,為表面水體和城市廢水中最頻繁出現(xiàn)的藥物與個(gè)人護(hù)理用品(PPCPs)之一[2],且對(duì)陸生脊椎動(dòng)物和魚(yú)類(lèi)的生長(zhǎng)已產(chǎn)生逆向作用[3].另外,污水處理過(guò)程的微生物代謝還可能引發(fā)DCF生物活性代謝物的釋放[4].

目前,去除水中 DCF的方法有吸附法,膜過(guò)濾,高級(jí)氧化法等[5-7].其中吸附處理是一種簡(jiǎn)單,快速,費(fèi)用低廉與可重復(fù)使用的方法.常用的吸附劑材料有二氧化硅、活性碳、沸石等[8-10].但這些吸附劑的吸附容量并不充分[11-12].

杯芳烴是由苯酚-甲醛縮合而成的一類(lèi)環(huán)狀低聚物,它具有可調(diào)節(jié)預(yù)成型的疏水性空穴,剛性構(gòu)象以及在其上緣(酚羥基),下緣(叔烷基)可進(jìn)行選擇性的官能團(tuán)取代[13-14].這些特性賦予了杯芳烴可與一系列有機(jī)或無(wú)機(jī)化合物形成主-客體配位絡(luò)合物,并因此被廣泛用做水介質(zhì)中對(duì)中性物種和金屬離子的捕捉劑[15-16].但杯芳烴的疏水性導(dǎo)致它在水中的溶解性很低,需要在有機(jī)溶劑中進(jìn)行液-液萃取,而且萃取之后還要進(jìn)行繁瑣的分離步驟[17-18].另一方面,溶液中杯[4]芳烴的吸附能力還受到構(gòu)象等因素的制約[19].上述原因在一定程度上限制了它們?cè)谒幚碇械膶?shí)際應(yīng)用.為此,近期有人采用共價(jià)或浸漬方式將杯[4]芳烴結(jié)合到聚合物基質(zhì)上或者接枝到 SiO2納米顆粒上,在改善杯[4]芳烴對(duì)有機(jī)污染物與重金屬離子的選擇性萃取的同時(shí)還可方便地將吸附劑從水中分離出來(lái)[20-22].

Amberlite XAD-4是聚苯乙烯型非極性大孔樹(shù)脂.由于這類(lèi)樹(shù)脂具有大的孔結(jié)構(gòu)和較高的比表面積和優(yōu)良的化學(xué),物理和熱穩(wěn)定性以及對(duì)水溶液不同pH值的耐受性,使其成為水中有機(jī)分子和金屬離子優(yōu)良的固相萃取材料[23-24].另外,Amberlite XAD-4樹(shù)脂聚合物網(wǎng)絡(luò)中的苯環(huán)殘基還可以容易地共價(jià)連接不同的功能基團(tuán),進(jìn)而衍生出具備優(yōu)異結(jié)合特性的吸附材料[25-26].

本文研究杯[4]芳烴與Amberlite XAD-4樹(shù)脂二種吸附材料優(yōu)點(diǎn)的相互結(jié)合,提高杯[4]芳烴-Amberlite XAD-4樹(shù)脂復(fù)合吸附材料的吸附能力.為此,通過(guò)重氮化反應(yīng)將杯[4]芳烴共價(jià)結(jié)合到 Amberlite XAD-4樹(shù)脂上.在杯芳烴修飾Amberlite XAD-4樹(shù)脂復(fù)合材料表征的基礎(chǔ)上,探討吸附劑的量,溶液 pH值等參數(shù)的變化對(duì)去除水中DCF的影響;采用準(zhǔn)一級(jí)與二級(jí)模型對(duì)吸附過(guò)程進(jìn)行擬合;計(jì)算不同溫度下吸附自由能(ΔG),焓(ΔH),熵(ΔS)等熱力學(xué)參數(shù).

1 材料與方法

1.1 材料

實(shí)驗(yàn)全部溶液為分析級(jí)試劑.NaOH,甲醛,二苯醚,丙酮,乙酸,乙醇等購(gòu)自天津江天化學(xué)品公司.雙氯芬酸(DCF)鈉鹽的純度≥98%(安陽(yáng)九州藥業(yè)有限責(zé)任公司),用于制備濃度為500mg/L的本體溶液,在使用前將其稀釋到所需濃度.實(shí)驗(yàn)用水為二次蒸餾水.

HZQ-QG振蕩器(中國(guó)哈爾濱東聯(lián)電子技術(shù)開(kāi)發(fā)有限公司),紫外-可見(jiàn)分光光度計(jì)(北京普析通用儀器有限責(zé)任公司).紅外光譜的數(shù)據(jù)由傅利葉變換紅外光譜儀(FTIR,NEXUS-5670, Nicolet, America)測(cè)得.采用S II Nano Technology Inc的TG/DTA6300型熱重分析儀檢測(cè)杯[4]芳烴修飾安珀萊特 XAD-4樹(shù)脂的熱穩(wěn)定性.用PHILIPS公司的XL30-ESEM環(huán)境掃描電鏡觀察修飾樹(shù)脂的表面形貌.

1.2 吸附劑的制備

1.2.1 杯[4]芳烴的合成 根據(jù)文獻(xiàn)方法合成了對(duì)叔丁基杯[4]芳烴[27-28],繼而以甲苯為溶劑,無(wú)水三氯化鋁為催化劑,在氮?dú)獗Ｗo(hù)下通過(guò)逆付-克反應(yīng)的脫烷基化得到去叔丁基的杯[4]芳烴.

1.2.2 杯[4]芳烴與Amberlite XAD-4樹(shù)脂的修飾 圖 1給出了杯[4]芳烴(II)在 Amberlite XAD-4樹(shù)脂(4)上的固定化過(guò)程[29-30].第 1步,在連續(xù)攪拌下將Amberlite XAD-4樹(shù)脂微球(5.0g)加入到由65% HNO3(10mL)和98% H2SO4(25mL)組成的混合物中,緩慢升溫至50℃反應(yīng)30min.降至室溫后將反應(yīng)混合物傾入到冰水中,過(guò)濾出硝化的樹(shù)脂微球,用二次去離子水洗滌硝化的樹(shù)脂數(shù)遍,直到不顯酸性.第2步,將硝化的樹(shù)脂加入到由37% HCl(16mL)和無(wú)水乙醇(20mL)組成的混合溶液中,攪拌下加入 SnCl2·2H2O(15g, 66.48mmol),在90℃加熱回流37h,使樹(shù)脂上的硝基還原為氨基.冷卻至室溫,依次用二次去離子水和2.0mol/L NaOH洗滌固體小球,以從生成的氨基樹(shù)脂(R—NH2)中去除副產(chǎn)物(R—NH3)2SnCl6.最后,用2.0mol/L HCl和過(guò)量二次去離子水洗滌氨基樹(shù)脂.第3步,將氨基樹(shù)脂懸浮在低于5℃冰水(400mL)中,有規(guī)律地將 1.0mol/L NaNO2和1.0mol/L HCl逐滴加入到反應(yīng)體系中進(jìn)行樹(shù)脂的重氮化反應(yīng)(混合物使淀粉-碘化鉀試紙變藍(lán)紫色為反應(yīng)終點(diǎn)).反應(yīng)結(jié)束,將重氮化樹(shù)脂過(guò)濾,冷水洗滌.第4步是去叔丁基杯[4]芳烴與重氮化樹(shù)脂的接枝,為此,將冰醋酸與丙酮(3:1)混合液降溫至 0～3℃,加入重氮化的樹(shù)脂與去叔丁基杯[4]芳烴(5mmol, 2.1g)反應(yīng)過(guò)夜,得到修飾樹(shù)脂的暗灰色小球,過(guò)濾,依次用二次去離子水與氯仿洗滌并在室溫下干燥.

1.3 分析方法

用 UV-vis分光光度計(jì)分析水溶液中DCF濃度,并且計(jì)算單位吸附劑對(duì) DCF的吸附量(公式1)和去除率(公式2).每次實(shí)驗(yàn)做平行3份.

式中, qe為吸附劑對(duì)吸附質(zhì)的吸附量,mg/g;V為溶液體積,mL;C0,Ce和Ct分別是吸附前,吸附平衡和t時(shí)刻溶液中DCF的質(zhì)量濃度,mg/L;m為杯[4]芳烴修飾 Amberlite XAD-4樹(shù)脂的量,g; r是DCF的去除率,%.

1.4 吸附等溫線實(shí)驗(yàn)

準(zhǔn)確稱(chēng)取 80mg杯[4]芳烴修飾樹(shù)脂,分別加入到 150mL濃度為 10,20,30,40,50,60mg/L的DCF水溶液中,然后置于一個(gè)振蕩器上,于溫度288,298,308,318K,160r/min搖動(dòng)4h,濾出吸附劑,在275nm波長(zhǎng)下用UV-vis分光光度計(jì)測(cè)定濾液中DCF的吸光度.根據(jù)Freundlich方程(公式3)與Langmuir方程(公式4)計(jì)算吸附等溫線的相關(guān)常數(shù).

式中, kf為Freundlich吸附系數(shù);n為Freundlich常數(shù);Xm和aL為L(zhǎng)angmuir常數(shù).

1.5 吸附動(dòng)力學(xué)實(shí)驗(yàn)

取一系列 250mL錐形瓶,各自加入 150mL初始濃度為20mg/L的DCF本體溶液,再分別加入80mg杯芳烴修飾樹(shù)脂,調(diào)節(jié)pH值為6.0,密封錐形瓶,以 160r/min速度振搖,一定時(shí)間間隔(20, 40,60,80,100,120,150,180,210,240,300,360,420, 480min)取樣,用UV-vis分光光度計(jì)在275nm下測(cè)定濾液中 DCF的吸光度,并且計(jì)算吸附劑對(duì)DCF的吸附量.

2 結(jié)果與討論

2.1 杯[4]芳烴修飾樹(shù)脂的理化性質(zhì)

2.1.1 杯[4]芳烴修飾樹(shù)脂的外形外貌 圖 2A是純Amberlite XAD-4樹(shù)脂放大30倍的SEM顯微圖像,可看到Amberlite XAD-4樹(shù)脂比較粗糙的表面.圖2B是杯[4]芳烴修飾Amberlite XAD-4樹(shù)脂的SEM圖像(放大30倍),可發(fā)現(xiàn)杯[4]芳烴覆蓋Amberlite XAD-4樹(shù)脂后得到的平滑與規(guī)則形狀的小球.

圖2 純Amberlite XAD-4樹(shù)脂與杯[4]芳烴修飾Amberlite XAD-4樹(shù)脂SEM圖像Fig.2 SEM images of pure Amberlite XAD-4TM and Amberlite XAD-4 resin immobilized calyx [4] arene

2.1.2 杯[4]芳烴修飾樹(shù)脂的FT-IR光譜 從圖3(A)可以明顯觀察到硝化樹(shù)脂苯環(huán)上硝基的反對(duì)稱(chēng)伸縮振動(dòng)(1529cm-1)和對(duì)稱(chēng)伸縮振動(dòng)(1349cm-1)特征峰,以及 C—N鍵的伸縮振動(dòng)(841cm-1)吸收峰.圖 3(B)中杯[4]芳烴修飾Amberlite XAD-4的特征吸收峰都有體現(xiàn),但又與二者單獨(dú)存在的 FT-IR不同.在 1242,1367, 1455,1507,1698cm-1處的峰與 C—O、C—N和N=N基團(tuán)的吸收有關(guān),顯示出Amberlite XAD-4樹(shù)脂的重氮化和杯[4]芳烴與樹(shù)脂的連接狀態(tài).

圖3 Amberlite XAD-4硝基衍生物與杯[4]芳烴修飾Amberlite XAD-4樹(shù)脂的FT-IR譜Fig.3 FT-IR spectrum of Amberlite amino derivative and Amberlite XAD-4 resin modified with calyx[4] arene

圖4 杯[4]芳烴修飾Amberlite XAD-4樹(shù)脂的熱重分析Fig 4 TG/DTA of Amberlite XAD-4 resin modifed with calyx[4]arene

2.1.3 杯[4]芳烴修飾樹(shù)脂的熱重分析 如圖 4所示的熱重分析(DTA/TG)曲線可知,在加熱初期,杯[4]芳烴修飾Amberlite XAD-4樹(shù)脂就有熱損失,例如在 68℃出現(xiàn)了一個(gè)小的吸熱峰,這是由于水分損失產(chǎn)生的;在 349℃出現(xiàn)一個(gè)大的放熱峰,可能源自杯[4]芳烴和 XAD-4樹(shù)脂上某些功能基團(tuán)的熱解;497℃處小的放熱峰預(yù)示杯芳烴骨架的開(kāi)裂;最后階段的熱重曲線下降到零,說(shuō)明修飾樹(shù)脂在此溫度下的汽化.

2.2 三種相關(guān)吸附劑的吸附性能比較

圖5給出了修飾樹(shù)脂與純Amberlite XAD-4樹(shù)脂吸附DCF吸附的比較,反應(yīng)條件為DCF濃度20mg/L,pH值6.0,接觸時(shí)間4h.

圖5 杯[4]芳烴修飾Amberlite XAD-4樹(shù)脂和Amberlite XAD-4樹(shù)脂及杯[4]芳烴去除DCF的比較Fig.5 The comparison for the removal of diclofenac by modified resin,Amberlite XAD-4 and calyx [4] arene

由圖5發(fā)現(xiàn),在同樣條件下修飾樹(shù)脂對(duì)DCF的吸附量比純Amberlite XAD-4樹(shù)脂及單獨(dú)杯[4]芳烴對(duì)DCF的吸附量大很多,而且隨投加量的增加差距更顯著.當(dāng)修飾樹(shù)脂的量增加到 80mg以上時(shí),去除率的增加趨于平緩并達(dá)到平衡.

一般認(rèn)為,溶液中杯[4]芳烴以錐體,部分錐體,1,2-交替及 1,3-交替的構(gòu)像存在[31],而且以錐體構(gòu)象的杯[4]芳烴分子最容易與客體分子形成包結(jié)絡(luò)合物[32].由于溶液中杯[4]芳烴的錐體構(gòu)象只是全部構(gòu)象體的一部分,而且并不是所有的杯[4]芳烴分子都參加與有機(jī)物的包結(jié)作用,表現(xiàn)為溶液中杯[4]芳烴對(duì)DCF的去除率不高.但當(dāng)杯[4]芳烴固定在Amberlite XAD-4樹(shù)脂上時(shí),由于構(gòu)象間的轉(zhuǎn)變受阻,大部分杯[4]芳烴分子以錐體構(gòu)象存在[33],而該構(gòu)象的空穴尺寸適合DCF這類(lèi)有機(jī)分子.因此,在疏水作用力驅(qū)動(dòng)下 DCF分子進(jìn)入樹(shù)脂固定的杯[4]芳烴的空穴內(nèi)而形成主-客體包結(jié)物(圖 6).另一方面,杯[4]芳烴上的羥基與DCF上的羧基可以形成氫鍵,導(dǎo)致杯[4]芳烴修飾Amberlite XAD-4樹(shù)脂對(duì)DCF的吸附性能的增大.至于修飾樹(shù)脂的量達(dá)到一定程度去除率達(dá)到平衡的原因,可能是當(dāng)修飾樹(shù)脂上吸附的DCF量達(dá)到一定濃度時(shí),修飾樹(shù)脂對(duì)DCF的作用相對(duì)變小,修飾樹(shù)脂上的DCF與溶液中剩余的DCF可能呈現(xiàn)相同的電性,而同種電荷之間形成靜電斥力,有礙于修飾樹(shù)脂對(duì)溶液中 DCF的吸附,造成了杯[4]芳烴修飾Amberlite XAD-4樹(shù)脂對(duì)DCF的吸附去除率隨著投加量的增加而趨于平緩.

圖6 化合物5與DCF的相互作用示意Fig.6 Proposed interactions of the adsorbent with DCF

2.3 pH值對(duì)杯芳烴修飾樹(shù)脂吸附DCF的影響

pH值決定著吸附劑上作用位點(diǎn)的化學(xué)形態(tài),因而對(duì)整個(gè)吸附過(guò)程,尤其是對(duì)于吸附劑的吸附容量有至關(guān)重要的作用.將DCF的初始濃度固定為20mg/L,修飾樹(shù)脂的量為80mg,反應(yīng)時(shí)間為4h,在不同 pH值(例如 1.0,2.0,3.0,4.0,5.0,6.0,7.0和9.0)進(jìn)行實(shí)驗(yàn),所得結(jié)果列于圖7.

由圖7可見(jiàn),當(dāng)溶液pH 值為 1到6時(shí),DCF的去除率均超過(guò)90%.一般來(lái)說(shuō),由于DCF中羧基(–COOH)的存在,它在低 pH值下表現(xiàn)為游離分子狀態(tài),這有利于DCF分子通過(guò)π-π作用進(jìn)入杯[4]芳烴及其多孔樹(shù)脂的空穴而被吸附.隨 pH值的增加,不斷增多的羥基負(fù)離子(OH–)將羧基中并逐漸成為帶負(fù)電荷的離子(–COO–),導(dǎo)致離子型DCF與分子態(tài)的DCF共存于溶液中.由于離子型DCF的羧基負(fù)離子是一種典型的吸電子基團(tuán),而Amberlite XAD-4樹(shù)脂苯乙烯聚合體的大 π鍵共軛體系容易供給電子,二者通過(guò)靜電吸附作用形成電子授-受體.這是 DCF吸附量增加的重要因素.但當(dāng)pH值＞6時(shí),溶液中大量增加的OH–使杯[4]芳烴苯環(huán)上的酚羥基脫去質(zhì)子形成負(fù)電荷,導(dǎo)致負(fù)電性的吸附劑與負(fù)離子型DCF產(chǎn)生靜電排斥,使DCF的去除率明顯下降,到pH值為9則去除率僅為1%.

圖7 不同pH值下的DCF去除率Fig.7 The removal rate of Diclofenac at different pH

2.4 杯芳烴修飾樹(shù)脂吸附DCF的等溫線

圖8給出了在DCF初始濃度為10mg/L到60mg/L,杯[4]芳烴修飾Amberlite XAD-4樹(shù)脂的量為80mg,溶液體積為150mL,溫度分別為288, 298, 308, 318K,恒溫160r/min搖動(dòng)4h條件下,杯[4]芳烴修飾Amberlite XAD-4樹(shù)脂對(duì)DCF的吸附等溫線.

由圖8可見(jiàn),在298K下,初始濃度為20mg/L的DCF在杯[4]芳烴修飾Amberlite XAD-4樹(shù)脂上的飽和吸附量達(dá) 34.02mg/g,并且修飾樹(shù)脂對(duì)DCF的飽和吸附量隨初始濃度的增大而增大.溫度升高,飽和吸附量略有下降,說(shuō)明此吸附過(guò)程為放熱過(guò)程,低溫對(duì)吸附有利.

2.5 杯芳烴修飾樹(shù)脂吸附DCF的動(dòng)力學(xué)

為了探討杯[4]芳烴修飾樹(shù)脂對(duì)DCF的吸附速率,在DCF初始濃度C0=20mg/L,pH6.0,吸附劑投加量為533.3mg/L條件下,分別在288,298,308, 318K下,研究了吸附劑與DCF接觸時(shí)間對(duì)吸附量的影響,結(jié)果如圖9所示.

圖8 杯[4]芳烴修飾Amberlite XAD-4樹(shù)脂對(duì)于DCF的吸附等溫線Fig.8 Adsorption isotherms of DCF on Amberlite XAD-4 resin modified with calyx[4]arene

圖9 杯[4]芳烴修飾的Amberlite XAD-4樹(shù)脂在不同溫度下對(duì)DCF的吸附速率.Fig.9 The adsorption rates of Amberlite XAD-4 resin modified with calyx[4]arene to the DCF under the various temperature

由圖9可見(jiàn),不同溫度下吸附劑對(duì)DCF的吸附速度有類(lèi)似的趨勢(shì).開(kāi)始時(shí)吸附速度較快,前20min去除率就達(dá)到了60%左右,在4h后達(dá)到吸附平衡狀態(tài).對(duì)于這個(gè)現(xiàn)象,可認(rèn)為開(kāi)始時(shí)吸附劑上有大量未被占據(jù)的表面位點(diǎn)促使吸附速度相當(dāng)快,但隨吸附量的增大,吸附劑上剩余表面位點(diǎn)逐漸減少,表現(xiàn)為吸附量的飽和.

為確定DCF在杯[4]芳烴修樹(shù)脂上的吸附速度,分別采用準(zhǔn)一級(jí)方程式(5)和準(zhǔn)二級(jí)方程式(6)模擬吸附過(guò)程的動(dòng)力學(xué).

式中: qe(mg/g)和qt(mg/g)是平衡與時(shí)間t杯[4]芳烴修飾樹(shù)脂吸附的DCF量;k1是一級(jí)方程式(5)的吸附速度常數(shù);k2是二級(jí)方程(6)的吸附速度常數(shù).

288～318K的qe和k1值可根據(jù)方程式(5)的ln(qe-qt)對(duì)時(shí)間t線性截距和斜率計(jì)算,方程式(6) t/qt對(duì)t的圖形應(yīng)當(dāng)給出一個(gè)線性關(guān)系,由此可得不同溫度下的qe與k2.上述2個(gè)方程的相關(guān)計(jì)算結(jié)果列于表1.

表1 不同溫度下動(dòng)力學(xué)模型回歸系數(shù)Table 1 Coefficients of kinetic model regression at different temperatures

由表1可看出,準(zhǔn)二級(jí)動(dòng)力學(xué)模型比準(zhǔn)一級(jí)模型更好地描述了杯[4]芳烴修飾 Amberlite XAD-4樹(shù)脂對(duì)DCF的吸附動(dòng)力學(xué).

2.6 杯芳烴修飾樹(shù)脂吸附DCF的熱力學(xué)

根據(jù)方程式(5)與(6),在288,298,308,318K,評(píng)估了杯[4]芳烴修飾Amberlite XAD-4樹(shù)脂吸附DCF的熱力學(xué)參數(shù).

式中,ΔH,ΔS,ΔG,T分別是焓, 熵, Gibbs自由能和絕對(duì)溫度, k0是吸附平衡常數(shù)L/mol,R是氣體常數(shù),8.314×10-3kJ/(mol·K),根據(jù)方程式(7), lnk0對(duì)1/T繪圖可得直線,由斜率與截距得到 ΔH = -22.49kJ/mol,ΔS=-60.25J/(mol·K). ΔH為負(fù),說(shuō)明杯芳烴修飾樹(shù)脂吸附DCF是放熱過(guò)程.由方程式(8),得到288,298,308,318K下的Gibbs自由能ΔG分別為-5.0537,-4.6606,-3.9358,-3.2749kJ/mol. ΔG為負(fù)說(shuō)明修飾樹(shù)脂對(duì)DCF吸附是自發(fā)過(guò)程,而且隨溫度升高 ΔG的絕對(duì)值變小,也證明低溫利于修飾樹(shù)脂對(duì)DCF的吸附.

關(guān)于低溫有利于杯[4]芳烴修飾樹(shù)脂對(duì)DCF吸附的原因,可能是當(dāng)溶液中的吸附質(zhì)在固體表面上吸附后,吸附質(zhì)分子從原來(lái)的三維自由運(yùn)動(dòng)變成限制在表面層上的二維運(yùn)動(dòng).根據(jù)熱力學(xué)第二定律,運(yùn)動(dòng)自由能的減少意味著熵的減少(ΔS＜0).由計(jì)算得到吸附過(guò)程中 Gibbs自由能減少(ΔG＜0),在等溫下,根據(jù)熱力學(xué)的基本關(guān)系式:ΔG = ΔH－TΔS,也可以推知ΔH＜0(放熱過(guò)程),由此可知降低溫度對(duì)吸附過(guò)程有利.

3 結(jié)論

3.1 不同的3種吸附劑對(duì)DCF的吸附結(jié)果表明,杯[4]芳烴修飾樹(shù)脂對(duì) DCF有最大的吸附容量,原因是杯[4]芳烴與樹(shù)脂的偶聯(lián)使得杯芳烴的優(yōu)勢(shì)構(gòu)象得以固定,促進(jìn)了修飾樹(shù)脂對(duì)水中 DCF的去除.在最佳條件下,杯[4]芳烴修飾樹(shù)脂對(duì)DCF去除率達(dá)到92.8%.

3.2 溶液pH值對(duì)吸附過(guò)程有很大影響,溶液pH為1到6,杯[4]芳烴修飾樹(shù)脂對(duì)DCFD的去除率超過(guò)90%,隨pH值增大,DCF 的–COOH變成負(fù)電荷離子(–COO–),而且吸附劑中杯[4]芳烴的酚羥基(–OH)脫質(zhì)子也形成負(fù)電荷(–O–),DCF負(fù)離子與吸附劑負(fù)電荷位點(diǎn)之間的靜電排斥力使DCF的去除率迅速減少,到pH=9,DCF去除率僅有1.1%.

3.3 根據(jù)準(zhǔn)一級(jí)與準(zhǔn)二級(jí)速度方程式對(duì)吸附數(shù)據(jù)進(jìn)行了回歸分析,得到了不同溫度下的吸附速度常數(shù)和平衡吸附量,在298K,2個(gè)速度方程的回歸系數(shù)都達(dá)到 97%以上,而且準(zhǔn)二級(jí)模型比準(zhǔn)一級(jí)模型更準(zhǔn)確地反映了吸附動(dòng)力學(xué).

3.4 等溫實(shí)驗(yàn)表明,Langmuir 和 Freundlich 等溫線與實(shí)驗(yàn)數(shù)據(jù)均有很好的擬合度,并且表明降低溫度有利于杯芳烴修飾樹(shù)脂對(duì)DCF的吸附.

3.5 熱力學(xué)參數(shù)的計(jì)算與理論分析表明ΔG＜0,表明杯[4]芳烴修飾Amberlite XAD-4樹(shù)脂對(duì)DCF的吸附是自發(fā)的,這意味著 ΔS＜0,進(jìn)而推知 ΔH＜0,預(yù)示吸附是一個(gè)放熱過(guò)程,溫度低對(duì)吸附有利.

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Removal of diclofenac on calyx [4] arene based Amberlite XAD-4 resin from aqueous solutions.

WANG Yue1, XIONG Zhen-hu1*, ZHOU Jian-guo2(1.Tianjin Key Laboratory of Aquatic Science and Technology, Department of Environmental and Municipal Engineering, Tianjin 300384,China；2.Department of Material Science and Engineering, Tianjin Institute of Urban Construction, Tianjin 300384, China). China Environmental Science, 2012,32(1)：81～88

The calyx [4] arene was synthesized and connected to Amberlite XAD-4 resin covalently through a diazotization bound. The structure of Amberlite XAD-4 resin base on calyx [4] arene was characterized using FT-IR, SEM and TG/DTA. The sorption results showed that Amberlite XAD-4 resin base on calyx [4] arene had much better removal to the diclofenac in aqueous solutions than Amberlite XAD-4 resin and calyx [4] arene which were presence alone in aqueous solutions. The removal rate of diclofenac increased rapidly with the calyx [4] arene modified Amberlite XAD-4 resin dosage. In the condition of DCF concentration was 20mg/L, when the Amberlite XAD-4 resin base on calyx [4] arene dosage came up to 80mg/L, the removal rate of diclofenac was 92.8% and reached equilibrium, the corresponding amount adsorbed was 34.02mg/g. Kinetic analyses were conducted using pseudo first-order and second-order models. The linear correlation coefficients and standard deviations of Langmuir and Freundlich isotherms were determined, and the results revealed that Langmuir and Freundlich isotherm were ftted the experimental data well. The thermodynamic parameters calculated indicated, ΔH and ΔG were negative, which predicated adsorption process of diclofenac on f Amberlite XAD-4 resin base on calyx [4] arene resin was exothermic and spontaneous.

calyx[4]arene；Amberlite XAD-4 resin；modification；diclofenac；adsorption

2011-04-10

國(guó)家自然科學(xué)基金資助項(xiàng)目(50878138)

* 責(zé)任作者, 教授, zhenhu.xiong@126.com

X703.5

A

1000-6923(2012)01-0081-08

王 月(1985-),女,天津市人,天津城市建設(shè)學(xué)院碩士研究生,主要從事水中有機(jī)污染物化學(xué)控制的研究.發(fā)表論文3篇.