摘要
本研究采用ZnCl2、KOH和尿素共同活化处理工业碱木质素,经高温碳化(700 ℃)制备得到木质素基高吸附性能材料(Zn-LB)。将Zn-LB用于亚甲基蓝和甲基橙染料溶液吸附实验,探究了染料种类、吸附温度、多元混合染料体系对Zn-LB吸附性能的影响。结果表明,Zn-LB的比表面积高达2 190.3
水是生态系统的基石,对于人类的存续和社会经济的可持续发展至关重要,但随着工业化的加速发展,产生了大量工业废水污染问题,未经过处理的有毒污染物会对动植物产生重大危害,给人类生产生活带来严重负面影
木质素作为自然界中分布广泛的天然高分子聚合物,在造纸行业中通常被认为是一种低价值的副产品,经常仅作为燃料进行燃烧产
本研究提出了一种简便的木质素基高效染料吸附材料制备策略,以工业碱木质素为原料,通过化学活化和碳化两步法,制备了高比表面积木质素基生物炭(Zn-LB)。同时采用亚甲基蓝、甲基橙等常见染料进行吸附实验,对Zn-LB吸附染料性能进行了评估。此外还探究了Zn-LB对二元混合染料体系下的阴阳离子选择性吸附性能。
工业碱木质素,山东龙力生物科技有限公司;甲基橙(MO),安徽泽升科技有限公司。氢氧化钾、氯化锌、尿素、盐酸、亚甲基蓝(MB)、藏红T(ST)和胭脂红(CR),上海麦克林生化科技有限公司。
扫描电子显微镜(SEM,SU-8000)及能谱仪,日本日立公司;傅里叶变换红外光谱仪(FT-IR,Tensor 27),德国布鲁克光谱仪器公司;X射线衍射仪(XRD,X'Pert'3 Powder),荷兰帕纳科公司;X射线光电子能谱仪(XPS,ESCALAB 250Xi),美国Thermo Scientific公司;全自动比表面及孔隙度分析仪(BET,NOVA 2200e),美国康塔仪器公司;紫外分光光度计(UV2600),日本岛津公司。
将3 g工业碱木质素、4.5 g KOH和3 g尿素溶解于64 g水中,300 r/min下搅拌混合均匀,加入3 g ZnCl2后继续搅拌6 h,所得溶液在60 ℃烘箱中干燥,将干燥后的固体放入管式炉中,通入氮气后,以5 ℃/min的升温速率逐步升温至700 ℃,保温2 h。待自然冷却至室温,取出碳化样品磨细,用1 mol/L盐酸洗涤,接着用去离子水洗涤直至滤液pH值=6~7。将洗涤后样品干燥,得到木质素基吸附材料,命名为Zn-LB。
配制质量浓度2 000 mg/L的亚甲基蓝(MB)和甲基橙(MO)溶液作为母液,后续吸附测试的染料溶液均为母液的稀释液。
分别稀释出2组不同浓度梯度的MB和MO溶液,对2组溶液用紫外分光光度计分别在MB(664 nm)和MO(464 nm)的最大吸收波长下测定吸光度,确定MB和MO的对应标准曲线。
Zn-LB吸附剂(质量浓度1 mg/mL)对MB(质量浓度600 mg/L)和MO(质量浓度600 mg/L)稀释液进行批量吸附实验。在室温条件下(搅拌速度600 r/min),分别设置不同取液时间(5 s、0.25 min、0.5 min、0.75 min、1 min、2 min、5 min、10 min、15 min、30 min、60 min、2 h、4 h、6 h、8 h、12 h),将所取溶液用0.22 μm滤膜过滤后进行紫外测试。调节波长为对应染料的最大波长,用紫外分光光度计测定各组滤液样品的吸光度,用于吸附动力学的研究。t时刻的样品吸附量(qt)采用
(1) |
吸附时间和吸附量采用准一级(
(2) |
(3) |
式中,C0表示MB或MO染料溶液的初始质量浓度,mg/L;Ct表示t时刻MB或MO的质量浓度,mg/L;V表示MB或MO溶液的体积,mL;m表示吸附剂的质量,mg。qe为平衡时的吸附量,mg/g;qt为t时刻的吸附量,mg/g;k1为准一级动力学速率常数,mi
稀释母液后获得多组质量浓度梯度为1 000~1 500 mg/L的MB溶液和1 400~1 800 mg/L的MO溶液,吸附剂质量浓度为1 mg/mL,将各组样品分别置于30、40、50 ℃的恒温水浴锅中,在600 r/min的条件下搅拌12 h,经滤膜过滤后,通过紫外分光光度计测量各组样品在最大波长处的吸光度。采用Langmuir(
(4) |
(5) |
式中,Ce为MB或MO吸附平衡时质量浓度,mg/L;qmax为MB或MO的最大吸附量,mg/g;KL 为Langmuir吸附等温常数;KF、n为吸附能力的Freundlich常数。
为进一步分析活化处理和高温碳化过程中碱木质素化学结构的变化,对Zn-LB和碱木质素进行FT-IR表征,如

图1 碱木质素和Zn-LB的红外光谱图
Fig. 1 FT-IR spectra of alkali lignin and Zn-LB
采用SEM对木质素基吸附材料的表观形貌进行观察,如

图2 (a)和(c) LB的SEM图;(b)和(d) Zn-LB的SEM图;(e)Zn-LB的EDS图
Fig. 2 SEM images of LB (a) and (c), SEM images of Zn-LB (b) and (d), EDS images of Zn-LB (e)
C | N | O | Zn |
---|---|---|---|
84.29 | 10.72 | 4.01 | 0.98 |

图3 Zn-LB和LB的XRD谱图
Fig. 3 XRD Spectra of Zn-LB and LB

图4 Zn-LB的XPS谱图
Fig. 4 XPS spectra of Zn-LB

图5 LB和Zn-LB的N2吸附-解吸等温曲线和孔径分布
Fig. 5 N2 adsorption-desorption isothermic curve and pore size distribution of LB and Zn-LB
SBET/( | Vtol/(c | Smic/( | Vmic/(c | Dp/nm |
---|---|---|---|---|
2 190.3 | 2.07 | 1 961.7 | 1.52 | 3.79 |
注 SBET为比表面积(BET法),Vtol为总孔容积,Smic为微孔比表面积,Vmic为微孔容积,Dp为孔径。
在初始质量浓度600 mg/L,吸附剂质量浓度1 mg/mL条件下,将LB和Zn-LB分别对MB和MO吸附60 min,结果见

图6 LB和Zn-LB对MB和MO吸附60 min后的对比图
Fig. 6 Comparison of the adsorption of MB and MO by LB and Zn-LB after 60 min

图7 Zn-LB对MB和MO吸附的准一级和准二级动力学
Fig. 7 Pseuso-first-order and pseuso-second-order Kinetics for MB and MO adsorption capacity of Zn-LB
染料 | 准一级动力学拟合 | 准二级动力学拟合 | ||||
---|---|---|---|---|---|---|
k1/mi | qe/(mg· | k2/mi | qe/(mg· | |||
MB | 0.158 8 | 47.3 | 0.715 1 | 0.014 8 | 602.4 | 1.000 0 |
MO | 0.502 5 | 99.4 | 0.923 6 | 0.037 3 | 598.8 | 1.000 0 |
采用Langmuir模型和Freundlich模型拟合了Zn-LB在303、313和323 K温度下对MB和MO的吸附数据,结果如

图8 MB和MO在Zn-LB上的吸附等温线
Fig. 8 Adsorption curves of MB and MO on Zn-LB
染料 | 温度/K | Langmuir模型 | Freundlich模型 | ||||
---|---|---|---|---|---|---|---|
qmax /(mg· | KL /(L·m | n | KF | ||||
MB |
303 313 323 |
1 273.1 1 316.5 1 345.9 |
0.434 0 0.422 0 0.651 7 |
0.998 6 0.998 3 0.999 1 |
20.94 18.60 17.11 |
979.8 987.2 1 006.7 |
0.946 3 0.911 8 0.946 9 |
MO |
303 313 323 |
1 732.4 1 663.7 1 604.4 |
0.412 3 0.752 1 0.321 3 |
0.996 3 0.996 4 0.996 9 |
26.80 15.45 33.89 |
1 376.3 1 259.5 1 340.5 |
0.558 9 0.907 3 0.509 2 |
染料 | 吸附剂 | 吸附量/(mg· | 参考文献 |
---|---|---|---|
MB | Zn-LB | 1 345.9 | 本研究 |
开心果壳活性炭 | 296.6 |
[ | |
椰壳活性炭 | 418.15 |
[ | |
活性炭/纤维素生物复合膜 | 103.66 |
[ | |
过氧化氢改性球磨生物炭 | 310.1 |
[ | |
木质素/Fenton污泥基磁性活性炭 | 301.0 |
[ | |
MO | Zn-LB | 1 732.4 | 本研究 |
壳聚糖复合膜 | 287 |
[ | |
莲藕生物炭 | 449 |
[ | |
纤维素衍生炭 | 337.8 |
[ | |
胺化南瓜籽粉 | 144 |
[ | |
ZnCl2络合分离木质素活性炭 | 263.6 |
[ |
采用Zn-LB对混合染料吸附选择性进行了研究。每种染料初始质量浓度为100 mg/L,混合染料体系中各染料按1∶1质量浓度比混合,在吸附剂质量浓度为0.5 mg/mL的条件下,对比吸附0.5 min后所得吸附前后光学照片及紫外光谱图,如

图9 Zn-LB吸附混合染料的颜色变化及相应的紫外光谱图
Fig. 9 Color changes and corresponding UV-Vis spectra of Zn-LB adsorbed mixed dyes
本研究以工业碱木质素为碳源,通过化学活化和高温碳化的方法制备了具有高吸附量和高比表面积的木质素基染料吸附材料(Zn-LB),并对其吸附性能进行了探究。
3.1 采用化学活化和高温碳化的方法合成的Zn-LB吸附剂比表面积和孔体积分别为2 190.3
3.2 Zn-LB对亚甲基蓝(MB)和甲基橙(MO)展现出良好的吸附能力,吸附过程符合准二级动力学模型和Langmuir等温吸附模型;同时研究还发现,Zn-LB对MB的吸附是吸热过程,升温有利于对MB的吸附,但升温不利于对MO的吸附。
3.3 Zn-LB对MB和MO的最大平衡吸附量分别为1 345.9和1 732.4 mg/g。同时,Zn-LB吸附材料的染料吸附量显著优于大多数生物质聚合物及活性炭材料。选择性吸附实验研究表明,Zn-LB对阴阳离子染料并不具明显倾向性,是一种对阴阳离子染料均友好的高效吸附材料。
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