Crystal Plane Regulation And Photocatalytic Performance Of Goethite

With the rapid development of economy and the expansion of the scope of human activities,the issue of soil pollution has become increasingly severe,necessitating the development of efficient and environmentally-friendly technologies for environmental protection.Among the various environmental remediation technologies,photocatalytic technology has emerged as a promising solution due to its ability to achieve thorough purification without causing secondary pollution,as well as its low energy consumption and economic feasibility.Soil minerals exhibit a high diversity,with iron-containing oxide minerals being particularly prevalent and widely distributed.Among all iron（hydrogen）oxide minerals,goethite（α-FeOOH）is the most abundant in surface soils,primarily due to its thermodynamic stability.Its nanoscale distribution is ubiquitous and not subject to climatic limitations.Given its abundance in soil,goethite has emerged as a popular research topic in environmental pollution control and other related fields.In this study,Al and Mn doped goethite were prepared by hydrothermal method,and their crystal surface appearance rates were different.Through the characterization of phase composition,microstructure,photoelectrochemical properties and photocatalytic performance,the crystal plane constraint mechanism of photocatalytic performance,the relationship between the crystal plane assignment form,composition ratio and photocatalytic performance were dissected and explained.1.Nanometer goethite was prepared by hydrothermal method..The composition of the products was analyzed under various conditions including different iron sources,p H values,reaction times,and temperature conditions.The results showed that goethite with a length ranging from 300-500 nm could be synthesized via hydrothermal treatment at 100°C for 12 hours,using iron chloride（Fe Cl3）as the iron source and under a p H of 12.8.2.The proportion of goethite with different crystal faces and its photocatalytic performance were studied.Various crystal plane guiding agents（ethanol,ethylene glycol,glycerol）have been employed to control the crystal plane orientation of goethite.Under the solvent condition of a 98:2 ratio of distilled water to ethylene glycol,nano goethite FG-2 with a（021）/（110）ratio of 0.14 can be synthesized.The removal rate of Cr（VI）by FG-2 reached 60.70%in 4 h,which was 61.00%higher than that of the non-crystal face directing agent system.Compared to the unmodulated crystal plane of FC,the apparent normalized catalytic reaction rate constant of FG-2 has increased by 7.28 times.The characterization results show that the improvement of Cr（VI）removal rate by FG-2 is mainly due to the lower adsorption energy of Cr ions on（021）crystal plane and the lower photogenerated electron-hole recombination rate on（021）crystal plane.3.The Al isomorphous substitution photocatalytic dominant crystal plane goethite and its photocatalytic performance were studied.Al-substituted goethite with varying proportions of crystal planes was synthesized through homogenous substitution of Al ions into the mineral lattice.Since the Al³⁺ion radius is smaller than the Fe³⁺ion radius,the Fe/Al-O distance along the（021）plane of Al-substituted goethite varies more than the Fe/Al-O distance along the（110）plane.As a result,the aspect ratio of goethite as the Al content increases.This further leads to an increase in the（021）/（110）ratio,which goes from 0.14 for FG-2 to 0.26 for FG-2/A-4.In the photocatalytic reduction experiment of Cr（Ⅵ）,the best removal performance was observed when the Al substitution content reached 4%,which corresponds to sample FG-2/A-4.The removal rate of Cr（VI）using sample FG-2/A-4 was found to be 83.80%for 4 h,which is38.06%higher than that of the undoped sample FG-2,which had a removal rate of 60.70%.The normalized apparent photocatalytic apparent reaction rate constant was 10.91 times higher than that of FC without regulating crystal plane and 0.28 times higher than that of FG-2.4.The Mn isomorphous substitution dominant crystal plane goethite and its photocatalytic performance were studied.Mn-substituted goethite with varying crystal plane ratios was synthesized using the hydrothermal method.The（021）/（110）crystal plane ratio could be increased to 0.17 when the Mn replacement amount was 4%（sample FG-2/M-4）.At the same time,FG-2/M-4 has the best performance of photocatalytic reduction of Cr.The removal rate of Cr（Ⅵ）can reach 79.01%at 4 h,which increases by30.16%compared with that of FG-2 to 60.70%,and is 1.94 times that of unregulated goethite FC.Its normalized apparent photocatalytic apparent reaction rate constant was 11.32 times higher than that of unmodulated crystalline FC and 0.33 times higher than that of FG-2.