CN116177685A - 一种掺硼金刚石电极净化污水并抑制副产物的方法 - Google Patents
一种掺硼金刚石电极净化污水并抑制副产物的方法 Download PDFInfo
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Abstract
本发明公开了一种掺硼金刚石电极净化水和/或污水并抑制电解过程中产生的高毒氯代副产物——氯酸盐(ClO3 ‑)和高氯酸盐(ClO4 ‑)的方法,具体包括以下步骤:S1电极预处理:采用物理和/或化学方法去除掺硼金刚石电极表面的非金刚石碳杂质,获得预处理电极;S2加入化学试剂处理污水:将碳酸盐或碳酸氢盐加入待处理的污水中,使污水中碳酸根或碳酸氢根的浓度为1mmol/L~10mol/L;S3氧化有机污染物:采用水处理设施将处理后的污水以指定电流密度或电压电解处理。本发明不仅方法简单,而且使用原料成本较低,有效提升有机污染物的降解效率,具有良好的经济效益和市场应用前景。
Description
技术领域
本发明属于电极制备技术领域,具体涉及一种掺硼金刚石电极净化污水并抑制副产物的方法。
背景技术
电化学氧化法是一种常用的水处理技术,具有以下优点:无需额外添加电解质(本身溶液的电导率高于272μS/cm时),可应用于多种非集中式水处理系统,利用其原位产生的氧化剂可高效降解有机污染物,尤其适用于处理稳定性高、毒害性大的有机污染物。
在电化学氧化法中,电极材料与降解途径和反应机理密切相关。根据有机污染物氧化的机理,可以将电极材料分为两大类:活性阳极(包括Pt、IrO2和RuO2)和非活性阳极(包PbO2、SnO2和BDD)。两类电极性能的不同与·OH的吸附焓有关,两者的初始反应均为H2O氧化生成羟基自由基(·OH),但是活性阳极会将·OH转变为氧化能力较差的氧化物或超氧化物(式1-1,1-2,1-3),即为化学吸附。而非活性阳极表面仅存在·OH的吸附位点(式1-4,1-5,1-6),即为物理吸附。
M(·OH)→MO+H++e- (1)
MO+R→M+RO (2)
MO→M+(1/2)O2 (3)
M(·OH)→M+H++(1/2)O2+e- (4)
M(·OH)→M+H2O2 (5)
M(·OH)+R→M+mCO2+nH2O+H++e- (6)
导电金刚石通过化学气相沉积法(CVD)等途径合成,结合预处理方法可以将杂质控制在稳定的范围内。经过掺杂、改性后的导电金刚石已作为电极材料广泛应用于各个领域,如环境降解、电合成、电催化和能量储存。而掺杂、改性的方向主要集中在不同杂原子掺杂、表面端改性、非金刚石碳的控制和生长基底。在降解有机污染物的过程中,通常需要高导电性的电极。通过在CVD生长期间添加适当的元素(例如B、N或P)来达到提高导电性的目的。在低掺杂水平(≤1019atom/cm3),表现为p型或n型半导体(取决于掺杂元素)。在高掺杂水平(≥1020atom/cm3),则表现为类金属,具有更高的导电性。B掺杂时的活化能(0.37eV)相对于其他元素(如氮1.7eV)低,因此掺杂浓度较高(1018–1021atom/cm3)。其他杂原子(N、P和S)掺杂浓度不高,一般<1019atom/cm3,导电性与半导体接近。当掺杂浓度≥1020atom/cm3,导电机理发生改变,表现为类金属性质,这是掺硼金刚石(BDD)最适用于电极材料的主要原因之一。
BDD电极具有·OH产率高的优点,目前已应用于多种实际水体,如地下水、池塘水、河流水、生活废水和市政废水等,同时包括含有多种难降解有机污染物的工业废水,如炼焦废水、造纸厂废水、含有持久性污染物的城市垃圾填埋场渗滤液、含有食品偶氮染料的废水、橡胶工业废水、橄榄油厂废水、低水平氮污染物(如氨离子和铵盐)的废水、含有ATZ的土壤洗涤废水、含铬化合物的工业废水、含全氟烷基酸的地下水、合成制革废水、调味品废水、纺织染厂废水、酒厂废水。研究表明,电化学氧化过程会形成多种有毒副产物,处理含氯水或废水时会生成氯代有机物、ClO3 -和ClO4 -。高毒性的氯代副产物是BDD电极应用的关键障碍之一。氯代有机物可通过阳极氧化、阴极还原、活性炭吸附去除,电解过程中氯代有机物出现峰值证明了此结论。因此控制高稳定性和毒性的ClO3 -和ClO4 -更为重要。
良策。
近年来,电化学生产H2O2取得了突破性进展,目前研究集中于两电子氧还原反应(2e-ORR),但两电子水氧化反应(2e-WOR)是更好的选择,因为其仅以水为反应物,相对于需要在水中溶解O2的2e-ORR更为简便,成本更低(2e-ORR通常需要贵金属,如Au、Pt和Pd)。2e-WOR研究较少的主要原因主要有三种。(1)H2O2的生成需要施加高于1.76V/SHE的电压,但仅少数的电极材料能在此电位下稳定运行。(2)由于·OH和H2O2的起始电势高于O2析出的起始电势,因此生成的H2O2容易被氧化,这也是2e-WOR表现出低法拉第效率的原因之一。(3)虽然2e-WOR是2e-ORR的逆反应,但2e-ORR的速率控制步骤是·OH和O2的还原反应,而2e-WOR受OOH·和O·形成步骤的限制。因此,研究较为深入的2e-ORR催化剂不能为筛选最佳的2e-WOR催化材料提供参考。
发明内容
本发明提供了一种方法,利用两电子水氧化反应(2e-WOR)协同掺硼金刚石(BDD)电极氧化有机污染物,提高有机污染物的降解效率,同时抑制有毒氯代副产物ClO3 -和ClO4 -的产生。
具体技术方案如下:
一种掺硼金刚石电极净化污水的方法,包括以下步骤:
S1电极预处理:采用物理和/或化学方法去除掺硼金刚石电极表面的非金刚石碳杂质,获得预处理电极;
S2加入化学试剂处理污水:将碳酸盐或碳酸氢盐加入待处理的污水中,使污水中碳酸根或碳酸氢根的浓度为1mmol/L~10mol/L;
S3氧化有机污染物:采用水处理设施将处理后的污水以指定电流密度或电压电解处理;
进一步的,S1中,所述的BDD电极的晶粒大小为微米级或纳米级;
进一步的,S1中,所述物理和/或化学方法选自酸溶液清洗、抛光法、电化学法中任意一种或几种;优选的,所述物理和/或化学方法选自电化学法;
进一步的,S2中,所述碳酸盐或碳酸氢盐选自NaHCO3、Na2CO3、KHCO3、K2CO3、Ca(HCO3)2中的任意一种或几种;
进一步的,S3步骤具体包括:将电解装置安装到水处理设施中,然后通入待处理的污水,使污水接触电极表面,以指定电流密度或电压电解污水,即得,其中,所述电解装置包括工作电极、辅助电极以及参比电极,其中,所述工作电极为BDD电极,所述辅助电极由不锈钢、铂、铜或其他导电材料制成,所述参比电极为饱和甘汞电极;
更进一步的,S3中,所述污水化学需氧量(COD)为10~10000mg/L;
更进一步的,S3中,所述指定电流密度为10~10000mA/cm2;
或更进一步的,S3中,所述电压为3~100V;
更进一步的,S3中,所述施加电压或电流时间为5min~4h;
更进一步的,S3中,所述电解在室温条件下进行;
更进一步的,所述电解处理包括污水中有机污染物在所述电极作用下被直接氧化或被电极产生的氧化剂氧化或被水分解产生的·OH氧化;
有益效果
采用本发明的方法制备电极并净化水/污水具有以下优点:
1.本发明采用物理和/或化学方法预处理电极能有效降低掺硼金刚石(BDD)电极中sp2组分含量,增强有机污染物的矿化能力,同时降低有毒氯代副产物的产量;本发明通过两个机理抑制ClO3 -和ClO4 -的生成:(1)H2O2抑制了ClO3 -和ClO4 -生成的关键中间产物——活性氯,(2)HCO3 -与ClO3 -竞争·OH反应,降低了ClO3 -向ClO4 -的转化速率。
2.通过向待处理水/污水添加碳酸盐或碳酸氢盐水溶液来催化BDD电极的2e-WOR反应,有利于将吸附性氧化物质扩散到溶液中,增强溶液本体中的有机污染物的降解效果。
3.本发明操作简便、经济实用。仅需添加一定浓度的含有碳酸根或碳酸氢根的水溶液,即可催化掺硼金刚石电极上的2e-WOR,进而达到促进有机污染物降解和抑制高毒性副产物的效果。
说明书附图
图1:本发明实验装置图;
图2:BDD电极上,电解质种类对H2O2浓度的影响;电解质种类对H2O2生成速率与法拉第效率的影响;
图3:添加NaHCO3、甲醇(猝灭剂)对BDD电极降解ATZ的影响:(a)降解速率,(b)降解反应的准一级动力学常数;
图4:NaHCO3的添加浓度对氯存在形式的影响:(a)活性氯浓度,(b)ClO3 -浓度,(c)ClO4 -浓度,(d)H2O2浓度的影响;
图5:NaHCO3对ClO3 -向ClO4 -转化的影响。
具体实施方式
下面结合具体实施例对本发明做进一步的说明,但本发明不限于下述实施例。
实施例1
一种掺硼金刚石电极净化水和/或污水的方法,包括以下步骤:
S1电极预处理:采用酸溶液清洗去除掺硼金刚石电极表面的非金刚石碳杂质,获得预处理电极,其中,所述掺硼金刚石电极晶粒大小为微米级或纳米级;S2加入化学试剂处理污水:将NaHCO3加入待处理的污水中,使污水中碳酸根或碳酸氢根的浓度为1mol/L;S3氧化有机污染物:在室温条件下,将电解装置安装到水处理设施中,然后通入待处理的污水,使污水接触电极表面,施加电压为20V,时间为30min,即得,其中,所述污水化学需氧量(COD)的浓度为100mg/L,所述电解装置包括工作电极、辅助电极以及参比电极,其中,所述工作电极为BDD电极,所述辅助电极由铂制成,所述参比电极为饱和甘汞电极。
实施例2
一种掺硼金刚石电极净化水和/或污水的方法,包括以下步骤:
S1电极预处理:采用酸溶液清洗去除掺硼金刚石电极表面的非金刚石碳杂质,获得预处理电极,其中,所述掺硼金刚石电极晶粒大小为微米级或纳米级;S2加入化学试剂处理污水:将NaHCO3加入待处理的污水中,使污水中碳酸根或碳酸氢根的浓度为10mol/L;S3氧化有机污染物:在室温条件下,将电解装置安装到水处理设施中,然后通入待处理的污水,使污水接触电极表面,施加电流为10000mA/cm2,时间为4h min,即得,其中,所述污水化学需氧量(COD)的浓度为10000mg/L,所述电解装置包括工作电极、辅助电极以及参比电极,其中,所述工作电极为BDD电极,所述辅助电极由铂制成,所述参比电极为饱和甘汞电极。
实施例3
一种掺硼金刚石电极净化水和/或污水的方法,包括以下步骤:
S1电极预处理:采用酸溶液清洗去除掺硼金刚石电极表面的非金刚石碳杂质,获得预处理电极,其中,所述掺硼金刚石电极晶粒大小为微米级或纳米级;S2加入化学试剂处理污水:将Na2CO3加入待处理的污水中,使污水中碳酸根或碳酸氢根的浓度为10mol/L;S3氧化有机污染物:在室温条件下,将电解装置安装到水处理设施中,然后通入待处理的污水,使污水接触电极表面,施加电压为50V,时间为2h min,即得,其中,所述污水化学需氧量(COD)的浓度为5000mg/L,所述电解装置包括工作电极、辅助电极以及参比电极,其中,所述工作电极为BDD电极,所述辅助电极由铂制成,所述参比电极为饱和甘汞电极。
实验例1:
为去除电极表面的sp2碳、增强亲水性,将电极在20mA/cm2(电流密度均按电极几何体积计算)的电流密度、1M NaClO4溶液中预处理20min。
本实施例采用三电极体系,工作电极为BDD电极(3×3cm2),辅助电极为铂片电极(99.99%纯度,3×3cm2),参比电极为饱和甘汞电极。工作电极与辅助电极的极间距设置为1.00cm。装置包括100mL未分隔的玻璃电解池、直流电源和磁力搅拌装置。实验装置如图1所示。
本实施例测试了三种常见的电解质水溶液(NaCl、NaHCO3和Na2SO4)对2e-WOR性能的影响。在10mM NaCl和Na2SO4水溶液中,H2O2浓度低于方法检出限(硫酸钛分光光度法),而NaHCO3可以有效促进H2O2的生成,如图2所示。
在NaHCO3水溶液中,H2O2的浓度快速升高,然后趋于稳定。H2O2浓度随着NaHCO3浓度的增加而升高。在10mM NaHCO3水溶液中电解10min时,H2O2的浓度为14.90μM,生成速率常数为0.17μM/(min·cm2),法拉第效率约为5.33%。10和50mM NaHCO3水溶液中,H2O2的生成速率提高了41.65%和134.71%。结果表明,BDD具有通过2e-WOR产生H2O2的能力,相较于NaCl和Na2SO4,BDD电极发生2e-WOR的最佳电解质为NaHCO3。
实验例2
为去除电极表面的sp2碳、增强亲水性,将电极在20mA/cm2(电流密度均按电极几何体积计算)的电流密度、1M NaClO4溶液中处理20min。实例采用三电极体系,工作电极为BDD电极(3×3cm2),辅助电极为铂片电极(99.99%纯度,3×3cm2),参比电极为饱和甘汞电极,工作电极与辅助电极的极间距设置为1.00cm。装置包括100mL未分隔的玻璃电解池、直流电源和磁力搅拌装置。实验装置如图1所示。
阿特拉津(ATZ)是使用最广泛的除草剂之一,对地表水和地下水的污染引起了人们的忧虑。本次选其作为目标污染物,用于判断2e-WOR对BDD电极降解有机污染物的效果及机理。依据《杂环类农药工业水污染物排放标准》(GB 21523-2008),实验中ATZ浓度设置为3mg/L(13.9μM)。将含有7mM NaCl和13.9μM ATZ的电解液以10mA/cm2的电流密度处理,取样体积2mL,同时加入1mL100mM Na2S2O3溶液用于猝灭样品中的·OH和活性氯。
2e-WOR对ATZ降解效果的影响见图3。7mM NaCl水溶液中,BDD电极上ATZ降解的准一级动力常数为3.64×10-4s-1,添加10和50mM NaHCO3后分别为4.63×10-4和5.60×10-4s-1,降解效率分别提高了27.2%和53.8%。添加100mM NaHCO3后ATZ降解的动力学常数为3.41×10-4s-1,降解效率降低了6.3%。HCO3 -和CO3 2-被认为是·OH的猝灭剂,但最近研究表明,HCO3 -与·OH反应形成更为复杂的氧化机制,涉及多种氧化物质,包括·O2 -、CO3 -·,HCO4 -和1O2,反应式如下。其中,CO3 -·对有机污染物的降解起着至关重要的作用。虽然CO3 -·氧化ATZ的能力相较于·OH弱(kCO3-.=3.7×106M-1s-1,k·OH=3.0×109M-1s-1),但CO3 -·自猝灭反应速率(1.2×106M-1s-1)明显低于·OH(5.5×109M-1s-1),导致在水溶液中CO3 -·的浓度远高于·OH。结合图3,可知添加一定浓度的NaHCO3有利于ATZ的降解。
OH+HCO3 -→H2O+CO3 -
·OH+CO3 -·→HCO4 -
CO3 -·+H2O2→HO2·
HO2·→H++·O2 -
甲醇猝灭剂仅会清除溶液本体中的氧化物质。加入甲醇猝灭剂后,7mM NaCl水溶液中ATZ降解的准一级动力常数为3.23×10-4s-1,相较于未添加甲醇时,降解动力学常数下降了11.3%,而添加10、50和100mM NaHCO3后,ATZ的降解动力学常数分别下降了44.9%、56.6%和47.8%,表明溶液本体中的氧化物质浓度增加。加入甲醇后,添加10、50和100mMNaHCO3时,ATZ的降解动力学常数分别为2.55×10-4、2.43×10-4和1.78×10-4s-1,相较于未添加NaHCO3时,分别降低了21.1%、24.8%和44.9%,说明电极表面的氧化物质浓度在降低。因此,NaHCO3的添加有利于把吸附于电极表面的氧化物质扩散到溶液本体中,促进了溶液本体中ATZ的降解。但ATZ含有三嗪环结构,属于缺电子有机污染物,当NaHCO3浓度较高时,体系整体氧化性降低,使ATZ的降解效果变差。由此可见,加入NaHCO3有利于有机污染物氧化降解。
实验例3
为去除电极表面的sp2碳、增强亲水性,将电极在20mA/cm2(电流密度均按电极几何体积计算)的电流密度、1M NaClO4溶液中处理20min。实例采用三电极体系,工作电极为BDD电极(3×3cm2),辅助电极为铂片电极(99.99%纯度,3×3cm2),参比电极为饱和甘汞电极,工作电极与辅助电极的极间距设置为1.00cm。装置包括100mL未分隔的玻璃电解池、直流电源和磁力搅拌装置。实验装置如图1所示。
2e-WOR对活性氯、ClO3 -和ClO4 -的影响如图4所示,当BDD电极电解7mM NaCl水溶液20min时,活性氯浓度为57.2μM,线性区域(0–20min)内活性氯的生成速率常数为0.32μM/(min·cm2)。活性氯浓度在线性区域快速增加,在20min达到最大值57.2μM,然后浓度逐渐降低,原因是Cl-浓度的降低使活性氯的氧化速率低于生成速率。当电解时间足够长时,所有的Cl-、活性氯和ClO3 -和均会转化为ClO4 -。
0.82%、15.37%和2.14%的Cl-分别转化为活性氯、ClO3 -和ClO4 -,溶液中活性氯、ClO3 -和ClO4 -浓度分别为57.23、1076.22和149.65μM,见图4a,b,c。ClO3 -的生成主要通过活性氯氧化,途径有电化学和化学两种。即活性氯与电解生成的·OH反应和活性氯的直接电子转移反应,虽然ClO3 -也可以通过Cl-在电极表面发生直接电子转移反应生成,但Cl-的直接电子转移反应对ClO3 -生成的贡献要远小于活性氯的电化学和化学反应。有研究表明,活性氯的存在使得ClO3 -的生成浓度升高,当电解液中不存在活性氯时,ClO3 -的生成受到较大程度的抑制。因此降低活性氯浓度对ClO3 -的抑制至关重要。当添加10mM NaHCO3时,活性氯浓度在20min时达到最高,浓度为22.71mΜ,相较于未添加NaHCO3时,活性氯浓度下降了60.3%。ClO3 -、ClO4 -和H2O2的浓度分别为967.95和91.26μM,生成速率常数分别下降了10.2%和39.2%。电解液中仍存在活性氯,因此ClO3 -的抑制效果不明显。当添加50mMNaHCO3时,活性氯的生成被完全抑制。电解20min时ClO3 -和ClO4 -的浓度为430.04和50.62μM,生成速率常数分别下降了60.0%和66.2%。添加100mM NaHCO3,电解时间为20min时,ClO3 -和ClO4 -的浓度为295.67和41.03μM,ClO3 -和ClO4 -的生成速率常数分别下降了72.5%和72.6%。ClO3 -和ClO4 -的生成不能被完全抑制,原因是2e-WOR不能抑制Cl-在电极表面的直接电子转移反应,但由于该部分所占比例较小。因此,利用抑制活性氯的生成是控制ClO3 -和ClO4 -浓度的有效途径。
实验例4
为去除电极表面的sp2碳、增强亲水性,将电极在20mA/cm2(电流密度均按电极几何体积计算)的电流密度、1M NaClO4溶液中处理20min。实例采用三电极体系,工作电极为BDD电极(3×3cm2),辅助电极为铂片电极(99.99%纯度,3×3cm2),参比电极为饱和甘汞电极,工作电极与辅助电极的极间距设置为1.00cm。装置包括100mL未分隔的玻璃电解池、直流电源和磁力搅拌装置。实验装置如图1所示。
室温下,低浓度的ClO3 -与H2O2反应可以忽略,即在NaHCO3存在的条件下,ClO3 -生成后仍会继续氧化为ClO4 -。有研究表明,ClO4 -的唯一生成途径为·OH与ClO3 -反应,并且该步骤为速率控制步骤。而HCO3 -可有效猝灭·OH。因此,判断NaHCO3对ClO3 -向ClO4 -转化的影响十分必要。
如图5所示,添加10mM NaHCO3时,ClO3 -的转化速率并未发生明显变化,ClO4 -的浓度为1397.60μM。当NaHCO3的添加量为50和100mM,电解时间为20min时,ClO4 -的浓度分别下降至477.12和324.97μM,ClO4 -的生成速率常数分别下降了63.9%和75.4%。由于HCO3 -和ClO3 -与·OH的反应速率常数相近,添加NaHCO3可有效降低·OH的浓度,导致ClO3 -向ClO4 -的转化速率降低。因此2e-WOR对ClO3 -和ClO4 -抑制作用的机理有两个方面。(1)2e-WOR产生的H2O2与活性氯反应,进而抑制ClO3 -和ClO4 -的浓度;(2)HCO3 -与ClO3 -竞争·OH反应,降低了ClO3 -向ClO4 -的转化速率。
·OH+HCO3 -→HCO4 - k=8.5×106M-1s-1
·OH+ClO3 -→ClO4 - k<1.0×106s-1。
Claims (11)
1.一种掺硼金刚石电极净化污水的方法,其特征在于,包括以下步骤:
S1电极预处理:采用物理和/或化学方法去除掺硼金刚石电极表面的非金刚石碳杂质,获得预处理电极;
S2加入化学试剂处理污水:将碳酸盐或碳酸氢盐加入待处理的污水中,使污水中碳酸根或碳酸氢根的浓度为1mmol/L~10mol/L;
S3氧化有机污染物:采用水处理设施将处理后的污水以指定电流密度或电压电解处理。
2.根据权利要求1所述掺硼金刚石电极净化污水的方法,其特征在于,S1中,所述的BDD电极的晶粒大小为微米级或纳米级。
3.根据权利要求1所述掺硼金刚石电极净化污水的方法,其特征在于,S1中,所述物理和/或化学方法选自酸溶液清洗、抛光法、电化学法中任意一种或几种;优选的,所述物理和/或化学方法选自电化学法。
4.根据权利要求1所述掺硼金刚石电极净化污水的方法,其特征在于,S2中,所述碳酸盐或碳酸氢盐选自NaHCO3、Na2CO3、KHCO3、K2CO3、Ca(HCO3)2中的任意一种或几种。
5.根据权利要求1所述掺硼金刚石电极净化污水的方法,其特征在于,S3步骤具体包括:将电解装置安装到水处理设施中,然后通入待处理的污水,使污水接触电极表面,以指定电流密度或电压电解污水,即得,其中,所述电解装置包括工作电极、辅助电极以及参比电极,其中,所述工作电极为BDD电极,所述辅助电极由不锈钢、铂、铜或其他导电材料制成,所述参比电极为饱和甘汞电极。
6.根据权利要求5所述掺硼金刚石电极净化污水的方法,其特征在于,S3中,所述污水化学需氧量(COD)为10~10000mg/L。
7.根据权利要求5所述掺硼金刚石电极净化污水的方法,其特征在于,S3中,所述指定电流密度为10~10000mA/cm2。
8.根据权利要求5所述掺硼金刚石电极净化污水的方法,其特征在于,S3中,所述指定电压为3~100V。
9.根据权利要求7或8所述掺硼金刚石电极净化污水的方法,S3中,所述施加电压或电流时间为5min~4h。
10.根据权利要求5所述掺硼金刚石电极净化污水的方法,S3中,所述电解在室温条件下进行。
11.根据权利要求5所述掺硼金刚石电极净化污水的方法,S3中,所述电解处理包括污水中有机污染物在所述电极作用下被直接氧化或被电极产生的氧化剂氧化或被水分解产生的·OH氧化。
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