碳热法合成纳米零价铁炭材料及去除水体中六价铬的方法研究

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摘要

本研究重点是要利用碳热法合成纳米零价铁/炭材料。以蔗糖和氯化亚铁的混

合液为前体物。在高温惰性气体中，蔗糖碳化、活化后形成多孔性炭颗粒材料，

二价铁被碳还原形成零价铁并包裹于炭颗粒中。

研究中将首先详细探讨纳米零价铁/炭材料的组成和形态，揭示纳米零价铁形

成过程和反应机理。通过改变碳热还原的温度，得到一系列纳米零价铁/炭材料。

利用 TEM、FTIR、XRD、BET 等手段对纳米零价铁/炭进行表征和分析。最终合

成的纳米零价铁/炭中，纳米零价铁呈球形，整体呈分散状随机分布在碳材料上，

团聚现象被大大降低。金属颗粒粒径的分布范围为 20-50nm，呈纳米级。随碳热还

原温度的升高，材料的铁含量逐渐增加，而 BET 比表面积和微孔孔容逐渐减小。

研究将进一步探索合成条件(铁碳物料比、处理温度、处理时间等)对最终材

料的物化性质的影响。碳热还原的温度选择 500°C，700°C，900°C 和1100°C，碳

热还原的时间分别为 0.5、1和3h，铁碳质量比为 1:3, 1:6 和1:12，热解的温度为

400°C 到800°C，处理时间为 0.5、1和3h。并以 Cr 为目标污染物来检测这些材料

对污染物的去除能力。结果显示，合成条件的改变对最终纳米零价铁/炭材料的晶

体结构、粒径分布、堆积密度、铁加载量以及对 Cr 的去除效率都有一定程度的影

响。参考材料对 Cr 的去除效率，将 Fe:C=1:6 的混合液，先 800°C 高温热解 0.5h，

再500°C 碳热还原 0.5h，制备的纳米零价铁/炭材料对 Cr 的降解能力最好。

最后，研究通过吸附平衡实验和吸附动力学实验，探讨了纳米零价铁/炭材料

对Cr 的去除机理，并考察了溶液 pH、离子强度、阴阳离子等因素对 Cr 去除性能

的影响。采用 Langmuir 和Freundlich 吸附等温方程对吸附平衡数据进行拟合。

Langmuir 方程拟合结果表明，500°C 条件下的纳米零价铁/炭的最大吸附量

(22.20mg/g)远大于其他纳米零价铁/炭材料。根据相关系数 R2，吸附过程更符合

Freundlich 等温吸附模型。通过动力学分析比较不同碳热还原温度下纳米零价铁/

炭材料与 Cr 的反应速率。吸附过程符合二级反应动力学模型，为物理吸附和化学

吸附相结合。其中 500°C 条件下的纳米零价铁/炭的表观速率常数 k2最大。纳米零

价铁/炭材料对 Cr 的去除是纳米零价铁和炭材料共同作用的结果。通过炭材料的吸

附，污染物被富集，纳米零价铁有更多的机会和 Cr 接触，从而获得比纳米零价铁

单独使用时更高的降解效率。纳米零价铁和 Fe2+都可将 Cr(VI)还原为 Cr(III)，而

且经还原而得到的 Cr(III)并未停留在溶液中，而是与 Fe(III)结合成氧化物或氢氧

化物共沉淀沉积在纳米零价铁/炭表面。纳米零价铁/炭降解 Cr 的过程中，酸性条

件更有利于 Cr 的降解而去除效果对离子强度的变化并不敏感。Zn2+,Ca2+,Mg2+,

Cu2+,SO42+和NO3-对Cr 去除效率没有明显的影响，但 PO43-和CO32+严重抑制了

Cr 的去除。

关键词：高温热解碳热还原纳米零价铁/炭 Cr 去除率

ABSTRACT

Starting with sucrose and ferrous chloride, nanoparticles of iron encapsulated in

carbon structure were synthesized using a carbothermal method. Sucrose undergoes

carbonization and activation to form a porous carbon material under high temperature

and N2 atmosphere. At the same time, zero-valent iron is reduced from high valent iron

and encapsulated in the carbon structure.

This research first intends to explore the mechanism of nanoscale zero-valent

iron/carbon formation. Sucrose was first carbonized at 800°C at the presence of iron

salts. The resultant product went through further carbothermal reduction from 500°C to

1100°C respectively to produce elemental iron. X-ray diffraction (XRD), Fourier

Transform Infrared Spectroscopy (FTIR) and Transmission Electron Microscopy (TEM)

were employed to study the properties of the final products. Nanoparticles containing

elemental iron in the size of 20-50 nm were formed and these particles were highly

dispersed and immobilized. In addition, BET surface area and pore volume analysis

revealed that porosity was formed. The formation of elemental iron increased with the

increase of temperature while BET surface area and micropore volume peaked at

500°C.

Secondly, the effects of carbothermal temperarure and treatment time, composition

of starting materials (Fe:C mass ratio), pyrolysis temperature and reaction time were

further investigated to study the properties of the synthesized products. The

carbothermal temperature changed from 500°C to 1100°C and treatment time used was

0.5, 1 and 3 h. Mass ratios of Fe and carbon were 1:3, 1:6 and 1:12 respectively. The

pyrolysis temperature range was from 400 to 800°C and treatment time used was 0.5, 1

and 3 h. Materials thus obtained were mostly powdered. X-ray diffraction (XRD)

patterns indicate that zero-valent iron was successfully produced from reduction of iron

oxides. Cr was employed as the target substance to test the removal efficiency.

Carbothermal temperature and treatment time, mass ratio, pyrolysis temperature and

reaction time all had significant influences on the physicochemical properties of the

materials and Cr removal. Based on the results obtained, the best conditions to obtain a

material with the highest Cr removal efficiency is using a starting material in the mass

ratio of Fe:C of 1:6, a pyrolysis temperature of 800°C for 0.5 h and then carbothermal

treated at 500°C for 0.5h.

Finally, the mechanism of Cr removal was discussed through adsorption equilibrium

and kinetic study, and the influence of pH, ionic strength (IS) and co-existing ions on Cr

removal were also tested. Synthesized materials demonstrated a high reactivity for

Cr(VI) removal. Langmuir and Freundlich isothermal adsorption equation were used to

fit the adsorption equilibrium data and the results suggested nanoscale zero valent

iron/carbon at 500°C had the biggest adsorption capacity (22.20mg/g) and the

Freundlich isothermal adsorption model fitted better with the process. Kinetics studies

were conducted to compare the rates of reaction for carbothermal materials. The

second-order kinetic model fit the experimental data better than first-order, suggesting

that the process involves chemical reaction mechanism and nanoscale zero valent

iron/carbon at 500°C showed the highest reaction rate constant of 7.70×10-5 L/(mg ·h).

Cr(VI) was removed through adsorption and reduction and Cr (III) was removed by

coprecipitation. Carbon’s hydrophobic nature leads to concentration of Cr in the vicinity

of the reactive iron surface. Nano zero Valent iron and Fe2+ were the main reductants.

The Cr removal efficiency decreased with the increased pH and was not sensitive to the

change of IS. Zn2+, Ca2+, Mg2+, Cu2+, SO42+ and NO3- showed no obvious influence, but

PO43- and CO32+ seriously hindered Cr removal.

Key Words: carbothermal synthesis, nanoscale zero valent iron,

carbon material, Cr removal.

中文摘要

ABSTRACT

第一章绪论···················································································································1

1.1 重金属铬污染·······································································································1

1.2 铬污染治理技术···································································································1

1.2.1 生物处理法···································································································1

1.2.2 化学处理法···································································································2

1.2.3 物化处理法···································································································2

1.3 纳米零价铁用于重金属污染···············································································3

1.3.1 纳米零价铁···································································································3

1.3.2 纳米零价铁用于水体重金属污染研究现状···············································4

1.3.3 纳米零价铁修饰技术研究进展···································································6

1.3.4 活性炭负载纳米零价铁···············································································8

1.3.5 碳热法合成纳米零价铁/炭复合材料·······················································10

1.4 研究意义及内容·································································································11

1.4.1 研究意义·····································································································11

1.4.2 研究内容·····································································································12

第二章碳热法合成纳米零价铁/炭材料及实验参数的优化·····································12

2.1 前言·····················································································································14

2.2 实验材料与分析方法·························································································14

2.2.1 实验材料·····································································································14

2.2.2 材料表征·····································································································14

2.2.3 分析方法·····································································································15

2.3 实验方法·············································································································16

2.3.1 碳热还原温度的影响·················································································16

2.3.2 碳热还原时间的影响·················································································16

2.3.3 铁碳比的影响·····························································································16

2.3.4 热解温度的影响·························································································16

2.3.5 热解时间的影响·························································································16

2.4 结果与讨论·········································································································17

2.4.1 碳热还原温度的影响·················································································17

2.4.2 碳热还原时间的影响·················································································24

2.4.3 铁碳比的影响·····························································································26

2.4.4 热解温度的影响·························································································28

2.4.5 热解时间的影响·························································································30

2.5 本章小结·············································································································32

第三章 Fe/C材料Cr去除机理及影响因素的探讨·······················································33

3.1 前言·····················································································································33

3.2 实验材料与分析方法·························································································33

3.2.1 实验材料·····································································································33

3.2.2 材料表征·····································································································33

3.2.3 分析方法·····································································································33

3.3 实验方法·············································································································35

3.3.1 投加量的影响·····························································································35

3.3.2 吸附平衡实验·····························································································35

3.3.3 吸附动力学实验·························································································35

3.3.4 pH对Cr去除效果的影响············································································35

3.3.5 离子强度对Cr去除效果的影响·································································36

3.3.6 阴阳离子对Cr去除效果的影响·································································36

3.4 结果与讨论·········································································································36

3.4.1 投加量的影响·····························································································36

3.4.2 吸附平衡实验·····························································································37

3.4.3 吸附动力学实验·························································································39

3.4.4 Cr去除机理探讨·························································································40

3.4.5 pH对Cr去除效果的影响············································································44

3.4.6 离子强度对Cr去除效果的影响·································································44

3.4.7 阴阳离子对Cr去除效果的影响·································································45

3.5 本章小结·············································································································46

第四章结论与展望·······································································································48

4.1 结论·····················································································································48

4.2 展望·····················································································································49

参考文献·························································································································50

在读期间公开发表的论文和承担科研项目及取得成果·············································60

致谢·································································································································61

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摘要：

摘要本研究重点是要利用碳热法合成纳米零价铁/炭材料。以蔗糖和氯化亚铁的混合液为前体物。在高温惰性气体中，蔗糖碳化、活化后形成多孔性炭颗粒材料，二价铁被碳还原形成零价铁并包裹于炭颗粒中。研究中将首先详细探讨纳米零价铁/炭材料的组成和形态，揭示纳米零价铁形成过程和反应机理。通过改变碳热还原的温度，得到一系列纳米零价铁/炭材料。利用TEM、FTIR、XRD、BET等手段对纳米零价铁/炭进行表征和分析。最终合成的纳米零价铁/炭中，纳米零价铁呈球形，整体呈分散状随机分布在碳材料上，团聚现象被大大降低。金属颗粒粒径的分布范围为20-50nm，呈纳米级。随碳热还原温度的升高，材料的铁含量逐渐增加，而BET比...

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