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图1 CSH与PCSH的(a) XRD图谱, (b) FT-IR图谱以及(c) N₂吸附脱附曲线

Fig. 1 (a) XRD patterns, (b) FT-IR spectra and (c) N₂ adsorption-desorption isotherms of CSH and PCSH

样品的FT-IR图谱如图1(b)所示。CSH样品在3462 cm^-1处的峰归因于水中羟基的伸缩振动, 并且其Si-O-Ca振动峰出现在972 cm^-1处^[16]。PCSH样品由于存在PEI的N-H伸缩振动峰, 使3449 cm^-1处峰的强度和宽度增加; 其在1480 cm^-1处新形成的峰应归于SiO^-···H···NH₂⁺氢键系统中NH₃⁺的对称变形^[17], 证明PEI通过氢键作用与水合硅酸钙成功接枝^[18]。此外, PCSH的Si-O-Ca伸缩振动峰转移至965 cm^-1, 说明引入PEI对水合硅酸钙结构产生了影响。此外, CSH样品在1448和874 cm^-1处出现了CO₃^2-的特征峰, 而PCSH样品中这两个峰的强度非常微弱。

CSH和PCSH的N₂吸附脱附等温线如图1(c)所示, 均属于典型的具有H3型滞后环的IV型吸附曲线, 其中PCSH在p/p₀=0.4~1.0的相对压力范围内的滞后环更加明显, 表明其具有更多的介孔结构。用BJH方法计算CSH和PCSH的平均孔径(D_BJH)、累积孔体积(V_BJH)和比表面积(S_BET), 结果见图1(c)插图。PCSH的V_BJH达0.83 cm³/g, 高于CSH的 0.78 cm³/g。PCSH的平均孔径只有7 nm, 仅为CSH (19.1 nm)的三分之一。更多小孔径使PCSH比表面积达到371 m²/g, 是CSH (240 m²/g)的1.5倍以上。

利用SEM观察样品的微观形貌。从图2(a, b)可见, CSH微观形貌主要由层状水合硅酸钙堆积组成的尺寸为3~5 μm的不规则多孔花状聚集体。而PCSH的聚集体尺寸在数百纳米和1~2 μm之间。与CSH相比, PCSH中的层状结构厚度更薄, 尺寸更小, 并且具有更多的开放性孔隙结构(图2(c, d)), 这与N₂吸附脱附表征分析结果一致。此外, CSH样品中还存在光滑立方体颗粒, EDS分析结果(图S1)显示其为CaCO₃, 而PCSH中则未观察到类似颗粒(图S2)。

图2

图2 (a, b) CSH与 (c, d) PCSH的不同放大倍率SEM照片

Fig. 2 Different magnification SEM images of (a, b) CSH and (c, d) PCSH

上述表征结果充分证明, 在水合硅酸钙合成过程中加入PEI, 显著影响了杂质含量及产物的微观形貌。长支链型大分子聚合物PEI不仅与硅酸根离子产生氢键作用影响其活度, 同时其具有的空间位阻效应还会在合成反应中对水合硅酸钙晶体的成核生长以及层状结构的分散与堆积产生极大影响, 进而诱导形成小尺寸的高度多孔层状结构^[19]。此外, PEI支链结构上的大量络合性氨基对游离Ca²⁺离子的识别结合则有效抑制了CaCO₃的形成。总之, 加入PEI提高了水合硅酸钙纯度, 并通过调控显微结构引入了更为丰富的吸附位点。考虑到PCSH中残余PEI对Cu(II)离子的强选择性螯合作用, 其对Cu(II)有望展示出高吸附能力^[20]。

2.2 样品的吸附性能

图3(a)为样品吸附量随时间的变化曲线。吸附实验在Cu(II)溶液为100 mg/L、吸附剂用量为0.5 g/L、初始pH 6的条件下进行。所有样品的吸附量在5~20 min内迅速增加, 这是由高浓度差与大量未反应活性位点共同导致。当接触时间从20 min延长到30 min, 由于溶液与吸附剂表面之间的Cu(II)浓度差逐渐减小, 样品吸附量的上升趋势也随之变缓。当接触30 min时吸附达到平衡, CSH与PCSH的吸附量分别达到127和195 mg/g, 去除率分别为64%和97%, PCSH显示出显著的吸附优势。

图3

图3 样品吸附性能表征

Fig. 3 Adsorption characteristics of samples

(a) Variation of adsorption capacity of samples with time; (b) Effect of pH on the adsorption capacity of PCSH; (c) Adsorption isotherms of samples; (d) Variation of adsorption capacity of samples with initial concentration of Zn(II)-Pb(II)

图3(b)显示了pH对PCSH吸附能力的影响, Cu(II)的初始浓度为300 mg/L, 吸附剂用量为0.5 g/L, 吸附4 h后取样。在低pH (pH 2~4)下, PCSH的吸附性能变差, 这是由于在低pH下PCSH的官能团(-NH₂)与氢离子反应发生质子化, 削弱了PCSH与Cu(II)离子的络合作用, 此时的吸附途径主要为依靠比表面积与孔结构的离子交换。在pH 5~6范围, PCSH表面官能团被激活, 活性官能团与金属离子开始产生配位作用, 从而使PCSH的吸附性能明显增加。此外, 由于pH>6.0时溶液中产生明显的沉淀现象, 后续实验的pH设定为5.0。

Cu(II)的初始浓度范围在100~1000 mg/L之间, 调整初始pH为5.0±0.3, 吸附剂用量为0.5 g/L, 吸附4 h后取样。如图3(c)所示, 所有样品对Cu(II)的平衡吸附量在低初始浓度时均迅速上升, 而随着浓度提升, 样品吸附量上升速率逐渐减缓。CSH与PCSH分别在初始浓度为900和1000 mg/L时接近吸附上限, 吸附量分别为276与575 mg/g。对样品的吸附等温线分别利用Langmuir模型(公式3)和Freundlich模型(公式4)进行拟合：

(3)$\frac{{{C}_{\text{e}}}}{{{q}_{\text{e}}}}=\frac{1}{{{K}_{\text{L}}}{{q}_{\text{m}}}}+\frac{1}{{{q}_{\text{m}}}}{{C}_{\text{e}}}$

(4)$\text{ln}{{q}_{\text{e}}}=\text{ln}{{K}_{\text{F}}}+\frac{1}{n}\text{ln}{{C}_{\text{e}}}$

其中, C_e为平衡浓度(mg/L), q_e为平衡吸附量(mg/g), q_m为饱和吸附量(mg/g), K_F为Freundlich吸附常数(mg/g), n为吸附强度, K_L为Langmuir吸附平衡常数 (L/mg)。

拟合曲线和拟合参数如图S3和表S1所示。样品在Langmuir等温模型中的相关系数R²(CSH, R²=0.9945; PCSH, R²=0.9982)均高于Freundlich模型(CSH, R²=0.867; PCSH, R²= 0.9450)。因此, 可以认为Cu(II)离子通过单层吸附均匀分布在材料的粗糙表面上。根据Langmuir模型可知, CSH和PCSH的理论饱和吸附容量分别为294和588 mg/g, 接近实验值276和575 mg/g。并且CSH与PCSH在Langmuir等温模型中吸附常数K_L分别为0.0200、0.0563(介于0和1之间), 这表明吸附过程是平稳且自发的。将本工作中样品的理论饱和吸附量与已报道的吸附剂的性能进行比较(表S2), 其中PCSH表现出最高的吸附能力。

为探讨水合硅酸钙在多元金属水溶液中对Cu(II)的吸附特性, 测试了其在不同干扰离子初始浓度(C_Zn=C_Pb=10, 20, 30 mg/L)的三元金属溶液中对Cu(II)(C_Cu=20 mg/L)的去除能力^[21]。初始pH调整为5.0±0.3, 吸附剂用量为0.5 g/L, 吸附30 min后取样。如图3(d)所示, 在无干扰离子存在的情况下, CSH与PCSH对溶液中Cu(II)的去除率分别为99.1%和99.3%。在Cu-Zn-Pb溶液中, 当Zn(II)-Pb(II)初始浓度由10 mg/L增大至30 mg/L时, CSH与PCSH的Cu(II)去除率分别由98.6%、98.9%降低至94.1%、98.6%, 整体呈现下降趋势, 这是由于溶液中Zn(II)与Pb(II)的存在导致了竞争吸附。与CSH相比, PCSH去除率的下降幅度十分微弱, 这可能是氨基对Cu(II)的强选择性吸附发挥了作用。上述结果表明, 在Zn(II)与Pb(II)存在的情况下, CSH与PCSH对Cu(II)吸附能力仍然保持在较高的状态, 并且PCSH具有更强的抗干扰能力。

2.3 吸附机理

为探究吸附机理, 对吸附后的样品进行了XRD测试, 如图4(a)所示。CSH-Cu和PCSH-Cu在2θ=16.2°、17.6°、32.2°和39.4°处均出现了一组对应于碱式氯化铜(CuCl₂ (Cu(OH)₂)₃, JCPDS 77-0116)的特征峰, 这表明PEI改性对所吸附Cu的物相组成无影响。但PCSH-Cu的XRD峰强明显高于CSH-Cu, 这与PCSH对Cu(II)吸附能力更强的结果一致。

图4

图4 吸附Cu后样品的表征

Fig. 4 Characteristics of Cu-absorbed samples

(a) XRD patterns; (b) Survey scans and high-resolution scans of (c) Cu2p, (d) N1s XPS spectra

图4(b~d)为吸附后样品的XPS谱图。吸附后两个样品的全谱(图4(b))中均出现了Cu2p特征峰。同时, Ca2p特征峰强度与吸附前相比有所减弱, 表明在吸附过程中均发生了离子交换。图4(c)为样品的Cu2p_3/2精细谱。在CSH-Cu中, Cu2p_3/2和相应的卫星峰分别出现在933.1~935.3和942.5~944.6 eV范围内。相比于CSH-Cu, PCSH-Cu发生了红移现象(Cu2p的峰向低结合能处移动了约0.2 eV), 这表明Cu(II)离子在结合过程中与相应的活性官能团相互作用(Cu-Cl、Cu-OH从-NH₂获得电子以补偿电荷)^[22]。为了进一步确认PCSH固定金属离子的吸附机制, 对吸附前后PCSH的N1s精细光谱进行分析。如图4(d)所示, 在PCSH的399.7 eV结合能处检测到属于-NH₂/-NH^-基团的N1s峰^[23]。吸附Cu(II)离子后, PCSH-Cu的N1s结合能移动到更高的位置(从399.7 eV到399.9 eV), 这表明PCSH对Cu(II)的化学吸附与N元素相关。正如前面所述, PEI对Cu(II)的选择性高于其他金属, 当PCSH接触Cu(II)后, 可能会有部分与Ca²⁺离子结合的氨基与其解离, 转而与Cu(II)离子发生结合, 进一步使N1s结合能受到影响。

以上结果说明, 离子交换对不同水合硅酸钙样品吸附过程均有所贡献。而对于PCSH, 除优异的微观结构可以提供大量活性位点外, PEI的氨基还显著增强了其化学吸附强度。上述因素共同作用, 使PCSH展现出较强的Cu(II)吸附能力。

2.4 催化性能

对吸附后的样品进行碱处理得到CSH-Cu-c和PCSH-Cu-c。图5为处理前后样品的SEM照片。图5(a)显示CSH-Cu保留了CSH的形貌特征, 呈现出片状堆积结构。而对于PCSH-Cu (图5(b)), 除原有的层状结构外, 还在相邻片层结构之间的高能角和边缘处出现了大量由微小的纳米颗粒组成的直径为100~150 nm球形颗粒。PCSH-Cu中所选区域的EDS结果显示, 点1处球状颗粒与点2处层状结构的元素组成比例相近(图S4), 表明溶液中的Cu(II)离子与吸附剂表面的氨基官能团结合后形成了由铜盐组成的球形颗粒。

图5

图5 (a) CSH-Cu, (b) PCSH-Cu, (c) CSH-Cu-c, (d) PCSH- Cu-c的SEM照片

Fig. 5 SEM images of (a) CSH-Cu, (b) PCSH-Cu, (c) CSH- Cu-c, and (d) PCSH-Cu-c

大量的Cu(II)离子被固定在PCSH的表面, 通过简单的碱处理可将其转化为水合硅酸钙-Cu-c复合材料。CSH-Cu-c (图5(c))的形貌未发生明显变化。而对于PCSH-Cu-c (图5(d)), 其前驱体表面的球形颗粒在处理后转化成由纳米棒组成的纺锤形多孔形貌。小尺寸纳米棒之间的堆叠诱导产生大量微小狭缝结构, 可以提供更多的活性位点, 并有利于反应过程中的传质。

通过分析碱热处理后样品的XRD图谱(图6(a))可以得知, CSH-Cu与PCSH-Cu中的碱式氯化铜在处理后几乎全部转化为Cu(OH)₂ (JCPDS 72-0140) 与少量CuO (JCPDS 80-1916)的混合物。此外, 与碱处理前样品相比, CSH-Cu-c与PCSH-Cu-c在2θ=29°附近归属于水合硅酸钙的主峰消失。这可能是由于吸附过程中样品内部的大量Ca(II)被溶液中Cu(II)的离子交换所替换, 随后样品中这些具有结构支撑作用的Cu(II)在碱热处理过程中参与反应, 进而破坏样品的基础晶体结构框架。

图6

图6 CSH-Cu-c与PCSH-Cu-c的(a) XRD和(b) FT-IR图谱

Fig. 6 (a) XRD patterns and (b) FT-IR spectra of CSH-Cu-c and PCSH-Cu-c

碱热处理后样品的红外光谱如图6(b)所示, 样品在3321~3575 cm^-1之间的吸收峰, 归属于表面自由水、金属氢氧化物(Cu(OH)₂)以及金属氧化物(CuO)的羟基伸缩振动^[24]。由于基础晶体结构框架被破坏, CSH-Cu-c在972 cm^-1处与PCSH-Cu-c在965 cm^-1处的Si-O-Ca振动峰减弱, 并且样品均在694 cm^-1处出现了归属于新形成的Si-O-Si对称伸缩振动峰^[25-26]。此外, PCSH-Cu-c在1480 cm^-1处归属于NH₃⁺的对称变形峰依然存在, 表明PEI与样品之间的结合十分稳定。

将CSH-Cu-c和PCSH-Cu-c用于催化PMS降解RhB, 具体实验条件为RhB, 20 mg/L; PMS, 0.12 g/L; 催化剂, 0.8 g/L; pH (7.0±0.3)。为比较降解反应动力学, 使用准一级反应动力学模型(公式(5))来描述RhB和随后的4-NP的降解。

(5)\[\text{ln}({{A}_{t}}/{{A}_{0}})=-k\times t\]

其中, A₀和A_t分别为初始时刻和t时刻降解产物的吸光度, k是准一级速率常数。

如图7(a)所示, 没有催化剂, RhB的降解非常缓慢; 添加CSH-Cu-c催化剂, 样品降解加快, 但20 min的降解率也仅达到32%。相比之下, PCSH- Cu-c对PMS的激活作用最为显著, 6 min内对RhB的降解率达到85%。表1比较了PCSH-Cu-c与文献报道其他催化剂的催化反应速率常数。本工作的PCSH- Cu-c的降解速率常数最高, 为其他文献报道结果的3~50倍(表1)。

图7

图7 CSH-Cu-c和PCSH-Cu-c催化PMS降解RhB的性能

Fig. 7 Degradation of RhB by PMS with CSH-Cu-c and PCSH-Cu-c

(a) RhB residue percentage; (b) Photo of catalytic device; (c) Catalytic performance of PCSH-Cu-c-M

表1 不同材料催化PMS降解RhB的速率常数(k)

Table 1 Rate constants (k) for the degradation of RhB by PMS with different catalysts

Catalyst	C₁/(g·L^-1)	C_PMS/(g·L^-1)	C_RhB/(mg·L^-1)	k/min^-1	Ref.
MPC	1	0.616	20	0.013	[27]
α-MnO₂/Pal	0.1	0.1	20	0.0204	[28]
Vis/BiVO₄	0.5	0.616	10	0.04	[29]
rGO-CoPc	0.3	0.616	10	0.288	[30]
CSH-Cu-c	0.8	0.12	20	0.036	This work
PCSH-Cu-c	0.8	0.12	20	0.7135	This work

C₁, C_PMS, and C_RhB are the concentrations of catalyst, PMS and RhB, respectively

为充分发挥PCSH-Cu-c快速降解染料的优势, 将样品分散在水中并使用聚酯膜过滤悬浮液中的样品粉末, 制备得到一种简易催化膜(PCSH-Cu-c-M)。以1 mg/L的RhB溶液作为降解对象, 在液体流速为3 mL/min的膜催化装置中测试其催化效率。如图7(b)所示, RhB溶液的颜色在经过简易催化膜后基本消失。处理后溶液的RhB浓度测试结果显示, RhB的降解率在溶液通量为15~45 mL范围区间内由90%迅速下降至73.6%(图7(c))。这可能是由于PCSH- Cu-c颗粒在聚酯膜上的附着力较差, 从而造成简易催化膜的结构被水溶液破坏(本实验中没有使用成膜剂)。随后, 由于RhB对催化剂的污染以及其他因素的影响, 其降解效率随着溶液通量的增加而缓慢下降。以上测试结果表明PCSH-Cu-c对于PMS具有显著的激活作用, 并且PCSH-Cu-c-M在实际应用领域中表现出极大的潜力。

通过XPS对反应前后PCSH-Cu-c表面元素和化学状态的变化进行了表征。如图所示, 样品中的铜离子(图8(a))与氧空位含量(图8(b))均发生变化, 表明都参与了反应。据相关文献报道, 金属基催化剂中活性位点的特征, 如表面羟基、金属离子与氧空位会对PMS活化产生重要作用^[31]。反应前样品的Cu2p与O1s分峰结果分别如图8(c, d)所示。根据理论计算, PCSH-Cu-c中的Cu⁺与氧空位含量分别为32.3%、64.6%, 显著高于CSH-Cu-c的23.1%、47.7%。以上表明, 与CSH-Cu-c相比, PCSH- Cu-c在催化反应中具有更多的活性位点。

图8

图8 样品表面元素和化学状态表征

Fig. 8 Suface elements and chemical status of samples

(a) Cu2p and (b) O1s XPS spectra of PCSH-Cu-c before and after reaction; (c) Cu2p and (d) O1s XPS spectra of CSH-Cu-c and PCSH-Cu-c before reaction

为进一步探究PCSH-Cu-c活化PMS机制, 在相同的RhB降解实验条件下, 本研究分别使用不同的自由基捕获剂(TBA：羟基自由基(•OH); EtOH：•OH和硫酸根自由基(SO₄^•-); NaN₃：单线态氧(¹O₂); BQ：超氧自由基(•O₂^-))进行了催化实验^[32]。如图9所示, 加入BQ与NaN₃均使样品的降解效率大幅下降; 加入TBA后降解率小幅下降, 而加入EtOH使下降程度更加明显。测试结果表明, •OH、¹O₂、SO₄^•-和•O₂^-均参加了降解反应, 并且•O₂^-是主要活性物质。

图9

图9 PCSH-Cu-c自由基捕获试验

Fig. 9 Free radical capture experiments of PCSH-Cu-c

据相关研究报道, 过渡金属离子、金属氧化物和羟基化金属物可以通过还原作用激活PMS, 产生大量具有强氧化性的羟基自由基、单线态氧、超氧自由基、硫酸根自由基, 从而有效降解有机污染物^[33⇓-35]。铜基催化剂的活化机制为^[36]:

(6)≡Cu(Ⅰ) + HSO₅^– → ≡Cu(Ⅱ) + SO₄^•– + OH^–

(7)≡Cu(Ⅰ) + HSO₅^– → ≡Cu(Ⅱ) + SO₄^2– + •OH

(8)HSO₅^– + SO₅^2– → SO₄^2– + HSO₄^– + ¹O₂

(9)2 SO₅^•– + H₂O → 2 HSO₄^– + 1.5 ¹O₂

(10)3 SO₅^•– + H₂O → 3 SO₄^2– + 2 •O₂^– + 5 H⁺

(11)RhB + SO₄^•–/•OH/•O₂^–/¹O₂ → Intermediates + CO₂ +H₂O

此外, PMS的活化能力还会受到催化剂中金属成分的负载量以及形态分布影响。本工作所制催化剂中含有大量的金属活性成分, 并且未经高温处理, 具有良好的晶型结构与小尺寸的晶粒分布, 因此表现出优异的催化能力。

进一步将CSH-Cu-c和PCSH-Cu-c用于催化NaBH₄还原降解4-NP实验, 具体条件: [4-NP]= 10^-4 mol/L; [NaBH₄]= 5×10^-3 mol/L; [催化剂]= 0.167 g/L; pH (11.0±0.3)。NaBH₄将4-NP降解为4-氨基苯酚的机制较为复杂, 在金属催化剂体系中, 可能是通过金属离子完成氢化物转移(从BH₄^-到4-NP), 从而促使还原反应高效进行^[37]。图10(a)显示使用PCSH- Cu-c作为催化剂, 3 min内4-NP的降解率达到87%, 反应混合物的亮黄色几乎变成无色(图10插图)。值得注意的是, 本实验在较低浓度的还原剂(n(NaBH₄)∶ n(4-NP)=50∶1)和催化剂条件下取得了理想的实验结果(表2)。

图10

图10 4-NP剩余浓度随时间的变化曲线

Fig. 10 Change of 4-NP residue percentage

Inset: photograph of the 4-NP solution after 3 min degradation

表2 不同材料催化NaBH₄降解4-NP的速率常数(k)

Table 2 Rate constants (k) for the degradation of 4-NP by NaBH₄ with different catalysts

Catalyst	C₁/ (g·L^-1)	C_NaBH4/(mmol·L^-1)	C_4-NP/ (mmol·L^-1)	k/(×10^-3, s^-1)	Ref.
CuO NLs	0.307	10	0.12	0.36	[38]
Ag-NP/C	0.333	6.667	4.7×10^-2	1.69	[39]
Cu₂₋_xSe/ rGO/PVP	2.5	62.5	0.125	2.3	[40]
Pd-FG	0.5	10	0.1	2.35	[41]
CSH-Cu-c	0.167	5	0.1	0.61	This work
PCSH-Cu-c	0.167	5	0.1	11.47	This work

C₁, C_NaBH4, and C_4-NP are the concentrations of catalyst, NaBH₄, and 4-NP, respectively

上述结果表明, 由PCSH吸附剂制备的催化剂在不同领域都表现出显著的催化性能, 这是因为样品表面含有大量的有效催化活性成分, 并且PCSH- Cu-c的形态较为均匀, 分散性较高, 呈现出有利于传质的微观结构。上述工作既证实了“金属污染物转化为催化材料”的实际应用潜力, 又揭示了桥接材料水合硅酸钙的相关性质对催化能力的重要影响。

3 结论

本工作利用粉煤灰为硅源制备的改性水合硅酸钙作为中间桥接材料, 探索了一条将水溶液中的铜元素转化为催化剂活性物质的途径。结果证明PEI对CaCO₃的形成有显著限制作用。与CSH相比, PEI的空间位阻作用使PCSH呈现出大比表面积 (371 m²/g)、细微孔径、高度多孔的优异显微结构, 为样品与吸附质的接触提供了更多的活性位点。结合氨基官能团对Cu(II)的高选择性络合, 使PCSH对Cu(II)的吸附量高达588 mg/g。因此, 相应催化剂的有效成分含量与形态也得到了改善。以PCSH为桥接材料制得的催化剂在PMS氧化反应(6 min时RhB降解率达到85%)和NaBH₄还原反应(3 min时4-NP降解率达到87%)中表现出优异的催化性能。本工作提供了一种适用于多领域的铜基高效催化剂, 实现了“金属污染物”转化为“催化材料”的可持续发展策略, 同时具有原料成本低、制备工艺简单、应用范围广等多种优点, 将有助于环境领域的治理改善。

补充材料

粉煤灰衍生水合硅酸钙PEI改性及吸附去除Cu(II)与催化降解有机污染物

汤亚^1,2, 孙盛睿², 樊佳^1,2, 杨庆峰³, 董满江², 寇佳慧¹, 刘阳桥²

(1. 南京工业大学材料科学与工程学院, 材料化学工程国家重点实验室, 南京210009; 2. 中国科学院上海硅酸盐研究所, 上海200050; 3. 中国科学院上海高等研究院, 上海201210)

图S1

图S1 CSH的EDS分析

Fig. S1 EDS analyses of CSH

图S2

图S2 PCSH的EDS分析

Fig. S2 EDS analysis of PCSH

图S3

图S3 CSH与PCSH在(a) Langmuir模型和(b) Freundlich模型中的吸附等温线拟合

Fig. S3 Linear fitting curves of (a) Langmuir model and (b) Freundlich model for isotherms of CSH and PCSH

图S4

图S4 PCSH-Cu的EDS分析

Fig. S4 EDS analyses of PCSH-Cu

表S1 Langmuir和Freundlich等温线拟合参数

Table S1 Langmuir and Freundlich isotherm fitting parameters

Sample	Langmuir model			Freundlich model
Sample	q_m	K_L	R²	n	K_F	R²
CSH	294.10	0.0200	0.9945	3.810	54.00	0.8670
PCSH	588.23	0.0563	0.9982	5.848	198.86	0.9450

表S2 文献中报道的各种吸附剂对Cu(II)的最大吸附能力比较

Table S2 Comparison of maximum adsorption capacities of various sorbents as reported in the literature for Cu(II)

Sample	q / (mg·g^-1)	S_BET/ (m²·g^-1)	Ref.
Activated carbon	10	921	[S1]
Modified SBA-15 mesoporous silica	46	317	[S2]
MCM-48	126	511	[S3]
Citrate-LDH	137	8	[S4]
Mesoporous silica	153	462	[S5]
Humulus scandens-derived biochars	221	450	[S6]
Steel slag-derived CSH	244	77	[S7]
Amorphous molybdenum sulphide	259	28	[S8]
NPCS-PEI	276	491	[S9]
CSH	294	240	This work
PCSH	588	371	This work

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Nickel-doped cobalt ferrite nanoparticles: efficient catalysts for the reduction of nitroaromatic compounds and photo-oxidative degradation of toxic dyes

Nanoscale, 2014, 6(14): 7959.

This study deals with the exploration of NixCo₁-xFe₂O₄ (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) ferrite nanoparticles as catalysts for reduction of 4-nitrophenol and photo-oxidative degradation of Rhodamine B. The ferrite samples with uniform size distribution were synthesized using the reverse micelle technique. The structural investigation was performed using powder X-ray diffraction, high-resolution transmission electron microscopy, energy dispersive X-ray and scanning tunneling microscopy. The spherical particles with ordered cubic spinel structure were found to have the crystallite size of 4-6 nm. Diffused UV-visible reflectance spectroscopy was employed to investigate the optical properties of the synthesized ferrite nanoparticles. The surface area calculated using BET method was found to be highest for Co₀.₄Ni₀.₆Fe₂O₄ (154.02 m(2) g(-1)). Co₀.₄Ni₀.₆Fe₂O₄ showed the best catalytic activity for reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH4 as reducing agent, whereas CoFe₂O₄ was found to be catalytically inactive. The reduction reaction followed pseudo-first order kinetics. The effect of varying the concentration of catalyst and NaBH₄ on the reaction rates was also scrutinized. The photo-oxidative degradation of Rhodamine B, enhanced oxidation efficacy was observed with the introduction of Ni(2+) in to the cobalt ferrite lattice due to octahedral site preference of Ni(2+). Almost 99% degradation was achieved in 20 min using NiFe₂O₄ nanoparticles as catalyst.

[38]

BHATTACHARJEE

, AHMARUZZAMAN

Green synthesis of 2D CuO nanoleaves (NLs) and its application for the reduction of p-nitrophenol

Materials Letters, 2015, 161: 79.

[39]

TANG

, VONGEHR

, MENG

Carbon spheres with controllable silver nanoparticle doping

Journal of Physical Chemistry C, 2010, 114(2): 977.

[40]

YANG

, ZOU

H Y

, HUANG

C Z

Synergetic catalytic effect of Cu_2-_xSe nanoparticles and reduced graphene oxide coembedded in electrospu n nanofibers for the reduction of a typical refractory organic compound

ACS Applied Materials & Interfaces, 2015, 7(28): 15447.

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[41]

WANG

, XU

, GAO

, et al.

Facile synthesis of well-dispersed Pd-graphene nanohybrids and their catalytic properties in 4-nitrophenol reduction

RSC Advances, 2014, 4(26): 13644.