干旱区生态环境知识资源中心(Arid): Photo-stimulated anoxic reduction of birnessite (delta-MnO2) by citrate and its fine structural responses: Insights on a proton-promoted photoelectron transfer process

Arid

DOI	10.1016/j.chemgeo.2020.120029
	Photo-stimulated anoxic reduction of birnessite (delta-MnO2) by citrate and its fine structural responses: Insights on a proton-promoted photoelectron transfer process
	Liu, Yuwei; Li, Yan; Li, Yanzhang; Chen, Ning; Ding, Hongrui; Jin, Song; Wang, Changqiu; Lu, Anhuai
通讯作者	Li, Y ; Lu, AH (corresponding author), Peking Univ, Sch Earth & Space Sci, Key Lab Orogen Belts & Crustal Evolut, Beijing Key Lab Mineral Environm Funct, Beijing 100871, Peoples R China.
来源期刊	CHEMICAL GEOLOGY
ISSN	0009-2541
EISSN	1872-6836
出版年	2021
卷号	561
英文摘要	The photo-enhanced dissolution of semiconducting birnessite by organic reductants prevalently occurs in the euphotic zones of natural aquatic systems. However, the underlying photoelectrons transfer mechanisms and kinetic factors are not fully understood. In this study, the anoxic photoreduction of delta-MnO2 (a phase analogue for natural birnessite) by citrate under simulated solar irradiation at pH 4.0, 5.5 and 7.0 was investigated, and the structural evolution of delta-MnO2 during the reaction was examined. The photoreduction of delta-MnO2 was observed at all three pHs. similar to 86.0% and similar to 32.7% Mn2+ was released into the solution at pH 4.0 and 5.5, respectively; while negligible amount of dissolved Mn2+ was produced at pH 7.0. Mn average oxidation state (AOS) in both the bulk and surface of delta-MnO2 lowered significantly with decreasing pH (3.39/2.56, 3.57/3.07 and 3.78/3.19 in bulk/surface at pH 4.0, 5.5 and 7.0, respectively). The increase in the photoreduction rate and extent of 8-MnO2 at lower pHs indicated the photoelectron transfer was pH-dependent. From the amount of reduced Mn(III/II) in structure and Mn2+ in solution, the average photoelectron transfer amount per mol Mn was calculated as 1.81, 0.95 and 0.22 at pH 4.0, 5.5 and 7.0, respectively. The retention of Mn(II) (-13% in content) in the structure of reacted delta-MnO2 was only observed at pH 4.0 rather than higher pHs. The photoreduction of Mn(IV) involved two successive steps of single-electron transfer to produce Mn(III) and further Mn(II), and the above results suggested the second-step photoelectron transfer was more effective under acidic conditions. The potential difference between the conduction band (CB) and MnO2/Mn2+ half-reaction was enlarged as pH decreased, which conduced to the optimal effectiveness of photoelectron transfer and thorough reduction of Mn(IV/III) under lower pH conditions. The pH-dependent Mn photoreduction occurred throughout the structure of delta-MnO2, whereas for the dark reaction, the influence of pH on the reduction extent only took effect on the surface. These observations implied the dark-reaction electron transfer predominantly occurred at the surface sites. By contrast, according to the semiconductor energy band theory, the excited CB photoelectrons were shared by all atoms in the lattice of delta-MnO2, and each Mn atom had equal chance to be reduced by photoelectrons. Furthermore, the accumulation of photo-reduced and large-size Mn(III/II) in the layer caused the spatial expansion of the in-plane crystallization, and could possibly alter the layer symmetry or even promote the long-term structural transformation towards tunneled Mn oxides. This work provides insights into the photocatalytic geochemical performance of the naturally-abundant birnessite, which is influenced by varied pH conditions on Earth's surface.
英文关键词	Birnessite Photoreduction pH effect Photoelectron transfer Structural evolution Semiconducting mineral
类型	Article
语种	英语
收录类别	SCI-E
WOS记录号	WOS:000608063900004
WOS关键词	BIOGENIC MANGANESE OXIDES ; MARINE BACILLUS SP. ; DESERT VARNISH ; ORGANIC-ACIDS ; ELECTRONIC-STRUCTURES ; HEXAGONAL BIRNESSITE ; MN(II) OXIDATION ; CARBOXYLIC-ACIDS ; RICH BIRNESSITE ; ROCK-VARNISH
WOS类目	Geochemistry & Geophysics
WOS研究方向	Geochemistry & Geophysics
来源机构	北京大学
资源类型	期刊论文
条目标识符	http://119.78.100.177/qdio/handle/2XILL650/347791
作者单位	[Liu, Yuwei; Li, Yan; Li, Yanzhang; Ding, Hongrui; Wang, Changqiu; Lu, Anhuai] Peking Univ, Sch Earth & Space Sci, Key Lab Orogen Belts & Crustal Evolut, Beijing Key Lab Mineral Environm Funct, Beijing 100871, Peoples R China; [Chen, Ning] Canadian Light Source, 44 Innovat Blvd, Saskatoon, SK S7N 2V3, Canada; [Jin, Song] Univ Wyoming, Dept Civil & Architectural Engn, Laramie, WY 82071 USA
推荐引用方式 GB/T 7714	Liu, Yuwei,Li, Yan,Li, Yanzhang,et al. Photo-stimulated anoxic reduction of birnessite (delta-MnO2) by citrate and its fine structural responses: Insights on a proton-promoted photoelectron transfer process[J]. 北京大学,2021,561.
APA	Liu, Yuwei.,Li, Yan.,Li, Yanzhang.,Chen, Ning.,Ding, Hongrui.,...&Lu, Anhuai.(2021).Photo-stimulated anoxic reduction of birnessite (delta-MnO2) by citrate and its fine structural responses: Insights on a proton-promoted photoelectron transfer process.CHEMICAL GEOLOGY,561.
MLA	Liu, Yuwei,et al."Photo-stimulated anoxic reduction of birnessite (delta-MnO2) by citrate and its fine structural responses: Insights on a proton-promoted photoelectron transfer process".CHEMICAL GEOLOGY 561(2021).