新技术利用太阳能制双氧水净化污水

诸平

现代的废水处理方法主要分为物理处理法、化学处理法和生物处理法三大类。物理处理法通过物理作用分离、回收废水中不解的呈悬浮状态的污染物(包括油膜和油珠)的废水处理方法，又可分为重力分离法、离心分离法和筛滤截留法等。属于重力分离法的处理单元有:沉淀、上浮(气浮)等，相应使用的处理设备是沉砂池、沉淀池、隔油池、气池及其附属装置等。关于废水处理方法的表述可以参考下表：

通过化学反应和传质作用来分离、去除废水中呈溶解、胶体状态的污染物或将其转化为无害物质的废水处理法被称之为化学处理法。在化学处理法中，以投加药剂产生化学反应为基础的处理单元是:混凝、中和、氧化还原等;而以传质作用为基础的处理单元则有:萃取、汽提、吹脱、吸附、离子交换以及电渗析和反渗透等。后两种处理单元又合称为膜分离技术。其中运用传质作用的处理单元既具有化学作用，又有与之相关的物理作用，所以也可从化学处理法中分出来，成为另一类处理方法，称为物理化学法。不论何种处理方法，其目的都是为了水的净化。是因为全世界有数十亿人缺乏干净的水源，而且主要问题是在发展中国家,水源经常被城市垃圾、工业垃圾以及农业废弃物所污染。但是废水中许多致病微生物和有机污染物可以使用过氧化氢（双氧水，H₂O₂）快速从水中消除并不会留下任何有害残留的化学物质。但是,过氧化氢的产生和传输在世界的许多地方却是一个挑战。

美国斯坦福大学（Stanford University）的研究人员和美国能源部斯坦福直线加速器中心（SLAC）国家加速器实验室（SLAC National Accelerator Laboratory）的SUNCAT界面科学和催化中心（SUNCAT Center for Interface Science and Catalysis），斯坦福同步加速器辐射光源（Stanford Synchrotron Radiation Lightsource）的科学家合作，已经研发出一种由可再生能源如传统的太阳能电池板生产过氧化氢的小装置。

克里斯·哈恩说：“我们的想法是开发一个电化学的电池,在现场生成氧气和过氧化氢,然后用过氧化氢氧化地下水当中对人体是有害的摄取的有机污染物。”相关研究于2017年3月1日在《反应化学和工程》（Reaction Chemistry and Engineering）杂志网站发表——Zhihua Chen,  Shucheng Chen,  Samira Siahrostami,  Pongkarn Chakthranont,  Christopher Hahn,  Dennis Nordlund, Sokaras Dimosthenis,  Jens K. Nørskov,  Zhenan Bao,  Thomas F. Jaramillo. Development of a reactor with carbon catalysts for modular-scale, low-cost electrochemical generation of H₂O₂. Reaction Chemistry and Engineering, 2017, 2: 239-245. DOI: 10.1039/C6RE00195E. First published online on 01 Mar 2017.

Abstract

The development of small-scale, decentralized reactors for H₂O₂ production that can couple to renewable energy sources would be of great benefit, particularly for water purification in the developing world. Herein, we describe our efforts to develop electrochemical reactors for H₂O₂ generation with high Faradaic efficiencies of >90%, requiring cell voltages of only ～1.6 V. The reactor employs a carbon-based catalyst that demonstrates excellent performance for H₂O₂ production under alkaline conditions, as demonstrated by fundamental studies involving rotating-ring disk electrode methods. The low-cost, membrane-free reactor design represents a step towards a continuous, modular-scale, de-centralized production of H₂O₂.

New device produces hydrogen peroxide for water purification

                     April 3, 2017                                                                

Now scientists at the Department of Energy's SLAC National Accelerator Laboratory and Stanford University have created a small device for hydrogen peroxide production that could be powered by renewable energy sources, like conventional solar panels.

"The idea is to develop an electrochemical cell that generates hydrogen peroxide from oxygen and water on site, and then use that hydrogen peroxide in groundwater to oxidize organic contaminants that are harmful for humans to ingest," said Chris Hahn, a SLAC associate staff scientist.

Their results were reported March 1 in Reaction Chemistry and Engineering.

The project was a collaboration between three research groups at the SUNCAT Center for Interface Science and Catalysis, which is jointly run by SLAC and Stanford University.

"Most of the projects here at SUNCAT follow a similar path," said Zhihua (Bill) Chen, a graduate student in the group of Tom Jaramillo, an associate professor at SLAC and Stanford. "They start from predictions based on theory, move to catalyst development and eventually produce a prototype device with a practical application."

       Sized to fit in one hand, this portable, low-cost device uses oxygen gas and water to produce hydrogen peroxide, which can be used to purify water in rural communities. Credit: Zhihua Chen/Stanford University    

In this case, researchers in the theory group led by SLAC/Stanford Professor Jens Nørskov used computational modeling, at the atomic scale, to investigate carbon-based catalysts capable of lowering the cost and increasing the efficiency of hydrogen peroxide production. Their study revealed that most defects in these materials are naturally selective for generating hydrogen peroxide, and some are also highly active. Since defects can be naturally formed in the carbon-based materials during the growth process, the key finding was to make a material with as many defects as possible.

"My previous catalyst for this reaction used platinum, which is too expensive for decentralized water purification," said research engineer Samira Siahrostami. "The beautiful thing about our cheaper carbon-based material is that it has a huge number of defects that are active sites for catalyzing hydrogen peroxide production."

Stanford graduate student Shucheng Chen, who works with Stanford Professor Zhenan Bao, then prepared the carbon catalysts and measured their properties. With the help of SSRL staff scientists Dennis Nordlund and Dimosthenis Sokaras, these catalysts were also characterized using X-rays at SLAC's Stanford Synchrotron Radiation Lightsource (SSRL), a DOE Office of Science User Facility.

"We depended on our experiments at SSRL to better understand our material's structure and check that it had the right kinds of defects," Shucheng Chen said.

Finally, he passed the catalyst along to his roommate Bill Chen, who designed, built and tested their device.

"Our device has three compartments," Bill Chen explained. "In the first chamber, oxygen gas flows through the chamber, interfaces with the catalyst made by Shucheng and is reduced into hydrogen peroxide. The hydrogen peroxide then enters the middle chamber, where it is stored in a solution." In a third chamber, another catalyst converts water into oxygen gas, and the cycle starts over.

Separating the two catalysts with a middle chamber makes the device cheaper, simpler and more robust than separating them with a standard semi-permeable membrane, which can be attacked and degraded by the hydrogen peroxide.

       A small device for hydrogen peroxide production (metal box pictured on the right) that is powered by two conventional solar panels. The low-cost device is being developed to make hydrogen peroxide on site for water purification in rural villages. Credit: Zhihua Chen/Stanford University    

The device can also run on renewable energy sources available in villages. The electrochemical cell is essentially an electrical circuit that operates with a small voltage applied across it. The reaction in chamber one puts electrons into oxygen to make hydrogen peroxide, which is balanced by a counter reaction in chamber three that takes electrons from water to make oxygen—matching the current and completing the circuit. Since the device requires only about 1.7 volts applied between the catalysts, it can run on a battery or two standard solar panels.

The research groups are now working on a higher-capacity device.

Currently the middle chamber holds only about 10 microliters of hydrogen peroxide; they want to make it bigger. They're also trying to continuously circulate the liquid in the middle chamber to rapidly pump hydrogen peroxide out, so the size of the storage chamber no longer limits production.

They would also like to make hydrogen peroxide in higher concentrations. However, only a few milligrams are needed to treat one liter of water, and the current prototype already produces a sufficient concentration, which is one-tenth the concentration of the hydrogen peroxide that you buy at the store for your basic medical needs.

In the long term, the team wants to change the alkaline environment inside the cell to a neutral one that's more like water. This would make it easier for people to use, because the hydrogen peroxide could be mixed with drinking water directly without having to neutralize it first.

The team members are excited about their results and feel they are on the right track to developing a practical device.

"Currently it's just a prototype, but I personally think it will shine in the area of decentralized water purification for the developing world," said Bill Chen. "It's like a magic box. I hope it can become a reality."                                                                

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