Xinxin Mo

                Ph. D. Candidate

               Email: xxmo@smail.nju.edu.cn

EDUCATION

◆ 09/2018 – now

Ph.D. Candidate in Geochemistry, School of Earth Sciences and Engineering, Nanjing University, China

◆09/2016－06/2018

MSc in Geochemistry, School of Earth Sciences and Engineering, Nanjing University, China

◆09/2012－06/2016

B.S. in Geology (Talent Training Class), School of Earth Sciences and Engineering, Nanjing University, China

RESEARCH INTERESTS

• Heavy metal sorption mechanisms at mineral/water interface (e.g. Ni, Zn, Cd);

• Synchrotron-based XAFS analysis;

• Stable Zn isotope analysis

TECHNIACAL SKILLS

• Proficiency in EXAFS data collection and analysis (e.g., shell fitting and LCF fitting); Beamtrips: BSRF (07/2016, 10/2016, 05/2017, 06/2018, 06/2019), SSRF (09/2016, 07/2017, 03/2019);

• Proficiency in conducting some analytical facilities, including ICP-OES, XRD, DRS, TEM, NMR;

• Master the metal (e.g., Zn) isotope measurements by MC-ICP-MS.

RESEARCH EXPERIENCE

◆07/2019-now

Ph.D. Candidate, School of Earth Sciences and Engineering, Nanjing University, China

Project: Determination   of Zn(Ⅱ) uptake mechanisms on palygorskite surfaces: A combined EXAFS and Zn   isotope techniques

Summary: Our previous study of   Ni(Ⅱ)-palygorskite system indicate a special precipitation mechanism induced   by palygorskite, indicating a certain relationship between uptake mechanism   and mineral surface/structure. In this research, the results demonstrated   that below pH 6, the sorption was dominated by outer-sphere and inner-sphere   surface complexation. Above pH 7.5, the EXAFS data suggested the formation of   Zn phyllosilicate type of precipitate, differing from the single   metal hydroxide type of precipitate in Ni(Ⅱ)-palygorskite system. However, its linear   type sorption isotherm is in consistent with Ni(Ⅱ)-palygorskite system. To   further determine the mechanisms especially at low concentration level, and   try to track the dynamic transition from surface complexation to surface   precipitation, we employed Zn stable isotope. Previous work with zinc in our   research group (Gou et al., 2018) demonstrates that clear relationships exist   between sorption mechanisms and isotope fractionation, suggesting a potential   feasibility to apply the metal stable isotope fingerprinting technique to   discriminate the sorption mechanisms. The sorption experiments and isotope   measurement are still ongoing.

◆01/2019-now

Project: Mechanism of CdⅡ)   sorption at the palygorskite-solution interface revealed by ¹¹³Cd nuclear   magnetic resonance spectroscopy

Summary: Solid-state nuclear   magnetic resonance (NMR) is an effective technique to obtain the information   on the bonding and chemical environment of an adsorbed species at   environmental mineral/water interfaces. In this study, Cd sorption onto   palygorskite was investigated as a function of reaction time, pH, ionic strength   and initial concentration. The results demonstrated that the Cd sorption was   dominated by inner-sphere surface complexation, without outer-sphere   complexation.  The NMR measurement are   still ongoing.

◆03/2018-08/2018

Project: Structural evolution   of heat-treated palygorskite revealed by ²⁷Al and ²⁹Si   magic angle solid-state nuclear magnetic resonance spectroscopy

Summary: In this study, ²⁷Al   and ²⁹Si magic angle solid-state nuclear magnetic resonance   (MAS-NMR) technology was employed in combination with scanning electron   microscopy (SEM), X-ray diffraction analysis (XRD), and infrared spectroscopy   (FTIR) to investigate the evolution of the morphology, structure, and physico-chemical   properties of palygorskite.

◆01/2016-01/2018

Project: Mechanisms of   Ni(Ⅱ) sorption at the palygorskite-solution interface revealed by EXAFS,   HRTEM, and DRS Investigation.

Summary: In this study, we investigated the mechanisms of Ni uptake with a   combination of macroscopic batch studies, transmission electron microscopy   (TEM), diffuse reflectance spectroscopy (DRS), and extended X-ray absorption   fine structure (EXAFS) spectroscopy.

The results demonstrated that below pH 6, the   sorption was dominated by outer-sphere and inner-sphere surface complexation.   Above pH 7.5, the EXAFS data suggested the formation of α–Ni(OH)₂   type of precipitate, in agreement with its linear type sorption   isotherm.A special finding is that the precipitates can form at   a very low Ni concentration (~ 0.07 mM), with the sorption density of   Γ=0.09 μmol m^-2, which corresponds to a 0.3% monolayer coverage   for palygorskite. In contrast, at this low level of Ni concentration, surface   precipitates have not form with γ-Al₂O₃. We assume that Ni can be directly induced to precipitate   on palygorskite surface (we call it “continuous nucleation”), differing from   the traditional adsorption-to-polymerization process on γ-Al₂O₃   surface (we call it “staged nucleation”). 

We further tested the role of mineral surface in the Ni precipitates formation. It was revealed that linear shape isotherm was also observed for Ni sorption on sepiolite, a clay with similar structure and chemical composition of palygorskite, indicating a similar reactivity of the both chain-structrue phyllosilicates. The findings not only improved the current understanding of metal sequestration at the mineral/water interfaces, but also provided new insights into the surface reactivity of clay minerals

PUBLICATION

HONORS AND AWARDS

CMS Ttravel Grant, The Clay Minerals Society (2020)

Outstanding Student Paper Award, Chinese Society of Mineralogy Petrology and Geochemistry, China (2019)

Second prize for postgraduate academic report, Soil Environment Professional Committee of Chinese Soil Society (2018)

Outstanding Student Paper Award, Chinese Society of Mineralogy Petrology and Geochemistry (2017)

Second-class academic scholarship, Nanjing University, Ministry of Education (2018, 2019)

First-class academic scholarship, Nanjing University, Ministry of Education(2016, 2017)

PRESENTATIONS AT CONFERENCES