Production Of Hydrogen,Zero-valent Iron And Ferroferric Oxide Octahedron By Alkaline Etching Al-fe Alloys

Clean energy and clean water are essential for a green and sustainable world.However,the excessive use of fossil energy not only depletes the fossil fuel reserves,but also causes serious environmental problems such as water pollution and climate change.Therefore,the development of clean and renewable energy sources and the research of efficient environmental remediation materials have attracted much attention.The use of clean hydrogen energy plays an important role in coping with climate warming.Since 2018,the development and application of hydrogen energy has been developing rapidly all over the world.Zero-valent iron(ZVI)is a major environmental remediation material,which is widely used to remove pollutants such as chlorinated hydrocarbons,heavy metals,dyes and toxic anions in water.Fe3O4 particles have stable properties,high catalytic activity and good magnetic properties,which are widely used in environmental remediation,magnetic fluid manufacturing and other fields.Here,the hydrolysis of Al-Fe alloys by alkaline solutions was investigated for production of hydrogen,super-active zerovalent iron(sZVI)and ferroferric oxide octahedron with excellent magnetic properties.Firstly,the effects of iron content of alloys,particle size of alloys,temperature,alkali concentration and NaCl addition on the hydrogen production by hydrolysis of Al-Fe alloy in alkali solution were investigated.The surface morphology,structure and composition of Al-Fe alloy and solid products during and after hydrogen production were analyzed by XRD,SEM,EDS,XPS and TEM.The mechanism of preparing hydrogen and high activity zero-valent iron(sZVI)by hydrolysis of Al-Fe alloy was proposed.The results show that the rate of hydrogen production by hydrolysis of Al-Fe alloy increases with the increase of alkali concentration,the hydrogen production value decreases with the increase of iron content in the alloy and the increase of particle size of the alloy.In 2 mol/L NaOH solution,the hydrogen production rate of Al-Fe alloy(Al-Fe20,10 g/L)with particle size of 20-40 mesh is 41.3 mL/(g·min)at normal temperature and pressure and the theoretical hydrogen production can be achieved.During hydrogen production,the Al of Al-Fe alloy dissolves continuously,and the micrometer-scale solid products with unique ravine morphology formed after hydrogen production,its specific surface area is 30-70 m2/g,i.e.sZVI.Secondly,the effects of aging temperature,reaction time and alkali concentration on the preparation of octahedral Fe3O4 from hydrogen-producing solid products of Al-Fe alloy in alkali solution were investigated.The results show that OH plays a dominant role in the growth direction of the material,and the increase of temperature accelerates the growth rate of the crystal plane.Proper OH-concentration,temperature and reaction time can make the material present regular octahedron morphology.The octahedral Fe3O4 with excellent magnetic properties can be obtained under the certain conditions such as 2 mol/L NaOH,90? and reaction time of 6 h.Finally,the removal performance of refractory organic dye orange 7(AO7)by sZVI(including particle size of precursor Al-Fe alloy,dosage of sZVI,AO7 concentration and initial pH and other factors)were investigated and compared with that of nano-zero valent iron(nZVI)and commercial reduced iron powder(cZVI).The results show that the removal of AO7 by sZVI is equivalent to that of nZVI and better than that of cZVI under the same conditions.sZVI has both high adsorption and reduction properties,in alkaline environment,the high adsorption capacity of sZVI can make up for the deficiency of reducibility,thus sZVI can maintain high removal rate of AO7 in the range of pH 3-11.Kinetics analysis showed that the removal of AO7 by sZVI accorded with pseudo-second-order adsorption kinetics and second-order reduction kinetics,the removal of AO7 is controlled by both adsorption and chemical reaction,but the reduction process is faster than adsorption process.The reaction products were analyzed and the way and mechanism of removing AO7 by sZVI was proposed.In addition,the removal of NO3-from water by sZVI reduction was studied.The selectivity of nitrogen in the reduction product was up to 40%.Compared with hydrogen,the storage and transportation of Al-Fe alloy is safer and more economical.Therefore,the preparation of hydrogen,ZVI with high activity and Fe3O4 with excellent magnetic properties by hydrolysis of Al-Fe alloy is expected to be widely used in the fields of resource recycling,clean hydrogen production and environmental remediation,and promote the world's green and sustainable development.