CN114920237B - 一种单层石墨烯气凝胶及其制备方法和应用 - Google Patents
一种单层石墨烯气凝胶及其制备方法和应用 Download PDFInfo
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Abstract
本发明公开了一种单层石墨烯气凝胶,其基本单元石墨烯为片状结构,单层片状结构的厚度<1.2nm。还公开了制备方法,包括以下步骤:取凝胶前驱体水溶液和晶体模板水溶液混合,注入模具后进行低温凝胶、超低温冷冻,脱除水分得到杂化气凝胶,热解使杂化气凝胶得以石墨化,然后去除晶体模板,干燥后即得。该单层石墨烯气凝胶的厚度非常薄、密度小、均一性好,厚度低于市面上常见石墨烯材料,电导率高达869.4S/m,且可规模化制备。另外,这种石墨烯气凝胶在碱性和中性条件下,也表现出了优异的氧还原电催化性能,可以作为碱性或中性条件下催化氧化还原反应的非金属催化剂,还可以成功应用于碱性和中性锌‑空电池中。
Description
技术领域
本发明属于石墨烯和气凝胶材料技术领域,尤其涉及单层石墨烯气凝胶及其制备方法和应用。
背景技术
石墨烯(Graphene)是一种以sp2杂化连接的碳原子紧密堆积成单层二维蜂窝状晶格结构的新材料。按照石墨烯的严格定义,石墨烯是一种晶体化的厚度为0.335nm的碳纳米片状材料,目前各界一般将小于10层,即理论厚度为3.35nm以内的碳纳米片归为石墨烯的范畴,而不局限于碳纳米片晶型程度。石墨烯材料因其独特的性质,在医学、电化学和能源等多个领域有广泛的研究和应用,引起了世界范围内广泛关注。在电化学领域,石墨烯因为具有优良的导电性和化学稳定性,特别适用于通过缺陷工程制备电催化剂。
石墨烯的光学、电学、力学等性质与石墨烯的层数密切相关,大多数应用,如海水净化,催化,药物递送等也与界面反应有关。因此根据石墨烯层数/厚度的不同,细分为单层石墨烯,双层石墨烯和多层石墨烯。人们渴望得到层数较少的石墨烯,甚至单层石墨烯,因为只有单层石墨烯才具有最大的理论比表面积,即2630m2/g,而层数每增加一倍,比表面积变减小一倍,同时,在10~12nm以下,石墨烯层数和电导率成负相关,超薄石墨烯具有更高的导电性能。然而,制备小于3层的石墨烯却十分困难,绝大部分报道的石墨烯属于3层及以上的石墨烯材料。另外,二维石墨烯容易发生聚集、堆叠,再次大大减少实际的可用面积,构造三维石墨烯气凝胶是解决这一问题的可行办法。已经报道的可能得到石墨烯气凝胶方法可分为两类,一类是用金属泡沫作为基底,利用气相沉积法(CVD)生长石墨烯,最后刻蚀基底,得到三维石墨烯气凝胶;第二种是利用氧化石墨烯GO作为基本构筑单元,通过冷冻浇筑、凝胶法、喷射法制备石墨烯气凝胶。前者涉及气相沉积中严格的条件控制和后期金属化学刻蚀等再处理,难以扩大规模;后者制备的石墨烯的性质受限于GO构筑单元,GO的质量决定了最后三维石墨烯的质量上限,均不能满足现在的多样化需求。
发明内容
本发明所要解决的技术问题是,克服以上背景技术中提到的不足和缺陷,针对现有石墨烯材料不理想的问题,采用特定类型的模板,提出了一种全新的单层石墨烯气凝胶及其制备方法,该方法具有绿色环保、易规模化、石墨烯层数少,比表面积高,导电性优异、界面反应传质快等特点;还提供了该单层石墨烯气凝胶作为碱性或中性条件下催化氧化还原反应的非金属催化剂的应用,以及用于碱性或中性锌-空气电池的应用。
为实现上述发明目的,本发明提供以下技术方案:
一种单层石墨烯气凝胶,所述单层石墨烯气凝胶的基本单元石墨烯为片状结构,单层片状结构的厚度<1.2nm。
优选的,所述单层片状结构在厚度以外的两个维度方向上尺寸>100nm;所述单层石墨烯气凝胶的碳纳米片表面含有孔径5~30nm的孔洞;所述单层石墨烯气凝胶的密度为2~30mg/cm3。
基于一个总的发明构思,本发明还提供一种单层石墨烯气凝胶的制备方法,包括以下步骤:
(1)凝胶前驱体和晶体模板分别在水中溶解,得到凝胶前驱体水溶液和晶体模板水溶液,取一定比例的凝胶前驱体水溶液和晶体模板水溶液混合,注入模具后进行低温凝胶化,得到杂化水凝胶;
(2)将所述杂化水凝胶进一步进行超低温冷冻,使其中水分固化,冷冻干燥脱除水分,得到含有所述凝胶前驱体和晶体模板的杂化气凝胶;
(3)将所述杂化气凝胶在含惰性气氛的保护条件下进行热解,使杂化气凝胶得以石墨化(凝胶前驱体在晶体化模板的空间限域作用下形成薄层碳纳米片),然后去除所述杂化气凝胶中的残留晶体模板,干燥后即得到所述的单层石墨烯气凝胶。
上述的制备方法,优选的,步骤(1)中所述凝胶前驱体为明胶、壳聚糖其中的任一种或多种。
优选的,步骤(1)中所述晶体模板为氯化钠、氯化钾、明矾其中的任一种或多种。模板优选为一类形状具有规则或近似规则平面的晶体结构、熔点温度在500℃以上、可被水或酸刻蚀、溶解脱模的材料。
优选的,步骤(1)中,所述凝胶前驱体水的溶液浓度为1wt%~20wt%,所述晶体模板水溶液的浓度为0.045g/mL~0.36g//mL。
优选的,步骤(1)中,所述凝胶前驱体水溶液和晶体模板水溶液的体积比为1:0.1-10。
优选的,步骤(1)中所述低温凝胶化的温度为0-10℃;步骤(2)中所述超低温冷冻的温度为-20℃~-80℃。
优选的,步骤(3)中所述惰性气体为Ar、N2其中的任一种或多种。
优选的,步骤(3)中的所述热解温度为500-2500℃。
优选的,步骤(3)中的所述杂化气凝胶残留晶体模板的去除方式为水洗或酸洗或碱洗。
优选的,所述单层石墨烯气凝胶的基本单元石墨烯为片状结构,在两个维度方向上尺寸>100nm,单层石墨烯的测试厚度<1.2nm。尺寸具体可通过晶体模板调节大小。
本发明发现利用具有规则平面的晶体模板,特别是立方模板,可以得到单层、双层石墨烯气凝胶材料。当大量立方体模板与凝胶共存时,受到立方模板的空间限域作用,绝大部分凝胶分子会被相邻的两个晶体平面压缩成膜,当空间限域作用足够强时,此膜的厚度只有一个原子层的厚度,在热解的作用下会碳化变成一个原子层厚度的碳纳米片,即单层石墨烯气凝胶。这里特别注意,得到单层石墨烯的关键在于模板类型的限制,区别于如球形模板或其它不规则模板等,只有具有规则平面的晶体才可以得到石墨烯,其中长方体晶体模板才具有最大的空间限域作用。
本发明的制备方法可以通过调节晶体模板含量来调控空间限域的作用大小,进而可以得到不同厚度碳纳米片的碳气凝胶,当晶体模板含量充足时,便可以得到单层石墨烯气凝胶,晶体模板可以通过简单的水洗去除,具有规模化制备的前景。
基于一个总的发明构思,本发明还提供一种单层石墨烯气凝胶作为碱性或中性条件下催化氧化还原反应的非金属催化剂的应用。
基于一个总的发明构思,本发明还提供另一种单层石墨烯气凝胶用于制备碱性或中性锌-空气电池的应用。
更优选的,利用上述单层石墨烯气凝胶作为空气电极催化剂制备锌-空气电池的空气电极,具体制备方法如下:将所述单层石墨烯气凝胶、PTFE(60wt%)、乙炔黑按照质量比为6:3:1混合得到混合物,用辊压机将混合物压在泡沫镍上,即得到空气电极。所述单层石墨烯气凝胶的密度为~2mg·cm-3。分别选择6M KOH和4M NH4Cl+2KCl作为碱性和中性锌-空气电池的电解液。
与现有技术相比,本发明的有益效果为:
1.本发明利用高温下晶体化模板空间限域气凝胶成为薄层碳纳米片的方法,制备得到石墨烯气凝胶的厚度非常薄、质量轻、均一性好,厚度远低于市面上常见石墨烯材料,厚度为1nm左右,考虑测试吸附物引起的厚度表观增加,按照一般认知,可以认为是单层石墨烯;经AFM证实构成石墨烯气凝胶的碳纳米片厚度可至1.07nm,扣除空气质量后,气凝胶密度为11.1mg/cm3。
2.本发明操作步骤简单、成本低廉、环境友好、易规模化,制备出来的成品石墨烯气凝胶层数少,比表面积高,导电性优异、界面反应传质快。
3.本发明制备得到的单层石墨烯气凝胶,得益于GAs-0.5的丰富活性中心、巨大表面积、内部多孔结构和电导率,单层石墨烯气凝胶和Pt/C在碱性和中性条件下的半波电位相当,具有与贵金属相当的宽pH氧化还原催化性能,可以作为碱性或中性条件下催化氧化还原反应的非金属催化剂,还可以成功应用于碱性和中性锌空电池中,并表现出了较高的开路电压。
附图说明
为了更清楚地说明本发明实施例或现有技术中的技术方案,下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍,显而易见地,下面描述中的附图是本发明的一些实施例,对于本领域普通技术人员来讲,在不付出创造性劳动的前提下,还可以根据这些附图获得其他的附图。
图1为实施例1中杂化凝胶中晶体模板充足时制备的单层石墨烯气凝胶SEM,保留长方体晶体模板前a、b以及脱除模板后c的图片;
图2为实施例1完全脱除氯化钠的单层石墨烯气凝胶样品TEM图片、AFM表征结果;
图3为实施例1完全脱除氯化钠的石墨烯气凝胶样品置放在桃花上的数码照片;
图4为石墨烯气凝胶和碳气凝胶在压力30MPa下的电导率;
图5为实施例1的Raman图谱和XPS N1s图谱;
图6为实施例1制备的单层石墨烯气凝胶和20wt%商业Pt/C在碱性和中性电解液中的线性扫描伏安法(LSV)曲线,饱和O2、1600rpm/min;
图7为实施例1制备的单层石墨烯气凝胶在碱性(6M KOH)和中性(4M NH4Cl+2KCl)中的锌-空气电池开路电压数码照片;
图8为实施例2本发明中杂化凝胶中晶体模板较少时制备的碳气凝胶SEM图片;
图9为实施例3杂化凝胶中没有晶体模板时制备的碳气凝胶SEM图片。
具体实施方式
为了便于理解本发明,下文将结合说明书附图和较佳的实施例对本发明做更全面、细致地描述,但本发明的保护范围并不限于以下具体实施例。
除非另有定义,下文中所使用的所有专业术语与本领域技术人员通常理解含义相同。本文中所使用的专业术语只是为了描述具体实施例的目的,并不是旨在限制本发明的保护范围。
除非另有特别说明,本发明中用到的各种原材料、试剂、仪器和设备等均可通过市场购买得到或者可通过现有方法制备得到。
实施例1:
一种单层石墨烯气凝胶,其基本单元石墨烯为片状结构,单层片状结构的厚度<1.2nm,该单层片状结构在厚度以外的两个维度方向上尺寸>100nm。
本实施例的单层石墨烯气凝胶的制备方法,制备杂化凝胶中晶体模板充足时的石墨烯气凝胶,包括以下步骤:
(1)配制凝胶前驱体和晶体模板的水溶液,取5g的明胶溶于50mL水中,取18g氯化钠溶于50mL水中,得到饱和氯化钠溶液;
(2)取等体积的氯化钠水溶液和明胶水溶液混合均匀,注入模具,4℃低温下凝胶化,得到杂化水凝胶;
(3)将步骤(2)的杂化水凝胶放入-80℃冷冻脱模,冷冻干燥得到杂化气凝胶;
(4)将步骤(3)得到杂化气凝胶在900℃、Ar条件下热解2h,得到石墨化的杂化气凝胶;
(5)将步骤(4)中得到的杂化气凝胶水洗三次,脱出易溶于水的晶体模板,干燥后得到单层石墨烯碳气凝胶GAs-0.5。
锌-空气电池组装方法如下:
锌-空气电池主要部分分为正极(空气电极)、电解液、负极(高纯锌片)三分部分。空气电极制备方法如下:GAs-0.5催化剂、PTFE(60wt%)、乙炔黑,按照质量比为6:3:1混合,用辊压机将混合物压在泡沫镍上,作为空气电极,催化剂密度为~2mg·cm-3。分别选择6MKOH和4M NH4Cl+2KCl作为碱性和中性锌-空气电池的电解液。
本实施例中杂化凝胶中晶体模板充足时,制备的单层石墨烯气凝胶SEM图片如图1,a图为部分脱除氯化钠的石墨烯气凝胶SEM图片,可明显看到立方形晶体和由碳纳米片构成的立方形腔体;b图显示石墨烯气凝胶表面存在粒径10~20nm的氯化钠晶体模板;c图为完全脱出氯化钠模板的石墨烯气凝胶SEM图片,可直观得出此时的碳纳米片很薄。
完全脱出氯化钠的石墨烯气凝胶样品TEM图和表征结果如图2,a图为其TEM图片,可观察到碳纳米片较薄,并有大量的孔缺陷,孔大小约15nm,与图1b纳米氯化钠模板大小一致;b图为AFM表征结果,从三维视图可得出纳米片的厚度较薄且均一,进一步的其厚度为1.07nm,低于报道的绝大部分石墨烯材料厚度,由于石墨烯表面常有污染物,一般可认为此厚度为单层石墨烯的厚度。
完全脱出氯化钠的石墨烯气凝胶样品如图3,a图为附有标尺的数码照片;b图为表示石墨烯气凝胶质量的数码照片,相应密度为11.1mg/cm3(扣除空气质量后);c图为紫叶桃花可轻松承载石墨烯气凝胶的数码照片,表明石墨烯气凝胶质量密度非常小。
图4为实施例1单层石墨烯气凝胶、实施例2多层石墨烯气凝胶、实施例3碳气凝胶中单层石墨烯气凝胶的电导率曲线,由图可知其实施例1的单层石墨烯气凝胶具有最高的电导率869.4S/m,表现出了与优异的导电性能和商业前景。
图5为单层石墨烯气凝胶GAs-0.5的Raman和XPS N1s图谱,相应的ID/IG=0.98,结合TEM的孔缺陷,可共同说明存在大量的碳边缘缺陷。同时无需额外氮源,所含有的掺杂氮来自凝胶前驱体,吡啶氮和石墨氮含量为1.7at%和2.4at%,碳缺陷、吡啶氮和石墨氮可作为氧化还原反应的活性中心,而单层石墨烯气凝胶的巨大比表面积和高电导率会极大的发挥活性中心的催化活性,电导率高达869.4S/m。
图6为商业贵金属催化剂20wt%Pt/C和单层石墨烯气凝胶GAs-0.5线性扫描伏安法(LSV)测试曲线,a-b为碱性KOH溶液,d-e为中性的磷酸缓冲液。如图5所示,得益于GAs-0.5的丰富活性中心、巨大表面积、内部多孔结构和电导率,单层石墨烯气凝胶和Pt/C在碱性和中性条件下的半波电位相当,具有与贵金属相当的宽pH氧化还原催化性能。
图7表明该单层石墨烯气凝胶可以作为锌-空气电池的空气电极催化剂,所组装的碱性和中性锌-空电池均表现出了较高的开路电压。
实施例2:
一种碳气凝胶的制备方法,制备杂化凝胶中晶体模板较少时的碳气凝胶,包括以下步骤:
配制凝胶前驱体和晶体模板的水溶液时,取5g的明胶溶于50mL水中,取9g氯化钠溶于50mL水中;操作同实施例1的步骤(2)-(5)。
杂化凝胶中晶体模板较少时,制备的碳气凝胶SEM图片如图8,其碳纳米片厚度不均一,碳纳米片多在10nm左右,较厚。
实施例3:
一种碳气凝胶的制备方法,制备杂化凝胶中没有晶体模板时的碳气凝胶,包括以下步骤:
配制凝胶前驱体和晶体模板的水溶液时,取5g的明胶溶于50mL水中,操作同实施例1的步骤(2)-(5)。
杂化凝胶中没有晶体模板时,制备的碳气凝胶SEM图片如图9,此时碳纳米片的厚度很大,不能称为石墨烯,其中9b图为9a图的放大图,碳片厚度~1μm,表面的颗粒为测试前喷金处理的表面覆盖金纳米颗粒。
Claims (5)
1.一种单层石墨烯气凝胶的制备方法,其特征在于,包括以下步骤:
(1)凝胶前驱体和晶体模板分别在水中溶解,得到凝胶前驱体水溶液和晶体模板水溶液,取凝胶前驱体水溶液和晶体模板水溶液混合,注入模具后进行低温凝胶化,得到杂化水凝胶;所述凝胶前驱体水溶液浓度为1wt%~20wt%,所述晶体模板水溶液的浓度为0.045g/mL~0.36g/mL;所述凝胶前驱体水溶液和晶体模板水溶液的体积比为1:0.1~10;所述低温凝胶化的温度为0-10℃;所述晶体模板为氯化钠、氯化钾、明矾其中的任一种或多种;
(2)将所述杂化水凝胶进一步进行超低温冷冻,使其中水分固化,冷冻干燥脱除水分,得到含有所述凝胶前驱体和晶体模板的杂化气凝胶;所述超低温冷冻的温度为-10℃~-80℃;
(3)将所述杂化气凝胶在含惰性气氛的保护条件下进行热解,所述热解温度为500-2500℃,使杂化气凝胶得以石墨化,然后通过水洗或酸洗或碱洗去除所述杂化气凝胶中的残留晶体模板,干燥后即得到所述的单层石墨烯气凝胶;
所述单层石墨烯气凝胶的基本单元石墨烯为片状结构,单层片状结构的厚度<1.2nm;
所述单层片状结构在厚度以外的两个维度方向上尺寸>100nm;所述单层石墨烯气凝胶的碳纳米片表面含有孔径5~30nm的孔洞;所述单层石墨烯气凝胶的密度为2~30mg/cm3。
2.根据权利要求1所述的制备方法,其特征在于,在步骤(1)中,所述凝胶前驱体为明胶、壳聚糖其中的任一种或多种。
3.根据权利要求1所述的制备方法,其特征在于,在步骤(3)中,所述惰性气氛为Ar、N2其中的任一种或多种。
4.一种由权利要求1-3中任一项所述制备方法制备得到的单层石墨烯气凝胶的应用,其特征在于,所述单层石墨烯气凝胶作为碱性或中性条件下催化氧化还原反应的非金属催化剂。
5.一种由权利要求1-3中任一项所述制备方法制备得到的单层石墨烯气凝胶的应用,其特征在于,所述单层石墨烯气凝胶用于制备碱性或中性锌-空气电池。
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