Post on 13-Jan-2017
transcript
Interaction between biochar and soil minerals --
revealed by electron microscopy
and X-ray photoelectron spectrometry
Yun Lin*, Paul Munroe, Stephen Joseph
School of Material Science and Engineering, University of NSW, NSW 2052 Australia
Lukas van Zweiten , Stephen Kimber
Wollongbar Primary Industries Institute, Industry and Investment NSW,
1243 Bruxner Highway, Wollongbar NSW 2477
The University of New South Wales
Outline
Introduction
Materials and Experimental Methods
Results and Discussion
�XPS examination of biochar surface
�SEM observation and EDS analysis on biochar surface
�Cross-sectional SEM and TEM observation at the interface
between biochar and mineral phases
Conclusion
Acknowledgements
Application of biochar as soil amendment:
Detailed studies of ancient Amazonian Terra Petra soils have revealed that anthropogenic original
black carbon with a high aromatic content has been stabilized, in part, due to interactions with
minerals, micro-organisms and soil organic matter (Brodowski et al. 2005; Liang et al. 2010).
The adsorption of soil materials to black carbon protects black carbon from oxidation and
decomposition (Nguyen et al. 2008). This implies the mineral attachment to biochar is important in the
stabilization process. Interactions and reactions happened immediately on application of biochar to
soil, especially at its surface.
The biochar surface properties play an important role in these interactions and reactions, and the
fresh biochar surface properties are controlled by the pyrolysis conditions applied and feed stocks
used.
Investigations on the mechanisms of mineral incorporation with biochar would therefore be useful to
reveal the interactions / aggregation of biochar and soil materials, in particular factors of soil affecting
biochar stability.
Introduction
Brodowskia S, Amelung W, Haumaier L, Abetz C, Zech W (2005) Morphological and chemical properties of black carbon in physical soil fractions as revealed by
scanning electron microscopy and energy-dispersive X-ray spectroscopy. Geoderma 128: 116-129
Liang B, Lehmann J, Sohi SP, Thies JE, O’Niell B, Trujillo L, Gaunt J, Solomon D, Grossman J, Neves EG, Luizão FJ (2010) Black carbon affects the cycling of non-
black carbon in soil. Organic Geochemistry 41: 206-213
Nguyen BT, Lehmann J, Kinyangi J, Smernik R, Riha SJ, Engelhard MH (2008) Long-term black carbon dynamics in cultivated soil, Biogeochemistry 89:295–308
Introduction
Techniques used:
X-ray photoelectron spectroscopy (XPS) test is an effective technique to provide the quality and
quantity information of surface chemical composition due to its capability to detect the
elements on surface less than 10nm depth , importantly for analysis of carbon-rich materials
such as carbon bonding states on biochar surface.
Scanning electron microscopy (SEM) provides data on surface morphology and, together with
energy dispersive spectrometry (EDS), can be used to determine the chemical composition of
any mineral particles attached.
Cross-sectional transmission electron microscopy (TEM) is able to visualize the structure of soil
aggregates and provides a means to analyze the mineral phases present at a nano-scale. Dual
beam Focus Ion Beam (FIB) was used to prepare TEM specimen.
Aim of the study:
To investigate both the biochar surface oxidation and the degree of interaction between the
biochar and clay/minerals, either in agronomic environment or under elevated temperature
Materials and Experimental Methods
The chicken litter (CL) biochar was pyrolysed with a highest temperature of treatment (HTT) of 450°C and held at this
temperature for 30 min using BEST Energies continuous slow pyrolysis process in the near absence of air. A small amount of
air comes into the reactor with feedstocks, which also included 20-30 wt% of woody material (sawdust). The CL biochar was
trialed for 9 months in a ferrosol soil in NSW where sweet corn was grown. The application rate in soil was 10
tonnes/hectare. After harvest, biochar particles were separated and tested.
Biochar-mineral complex (BMC): A biochar from an acacia saligna wood pyrolysed at approximately 400°C for 4hrs, named
as saligna biochar, was activated with 1M phosphoric acid (without separation after reaction), and then mixed with clay from
a local brickworks (high in calcium sands, apatite and illite), minerals (a high loading of manganese dioxide and waste
illemnite) and local chicken litter (with sawdust). Water was added to the mixture so that it had a moisture content of about
30%. This mixture was stirred at the temperature of 80°C for 2 hrs and then placed into a batch reactor. The material was
brought up to ~220°C in approximately 1 hr and then held at this temperature for 3hrs.
All sample pieces were dried at 60°C before use and mounted in resin and polished. Samples were coated with Cr to
improve the surface conductivity, and examined using scanning electron microscopy (SEM) with energy X-ray dispersive
spectrometry (EDS) facilities attached.
An electron transparent section at the interface between the biochar and mineral phases was prepared using a focused ion
beam (FIB) microscope. Samples were examined by transmission electron microscopy (TEM). Scanning TEM mode (STEM)
was used to perform EDS mapping , line scans (points taken at 1 nm intervals) and points analysis in region of interest.
The atomic concentrations of elements, as well as carbon chemical bonding state at biochar surfaces, were investigated by
XPS (ESCALAB-220i-XL manufactured by VG Scientific UK) with a monochromatic Al Kα X-ray source ( hν = 1486.6eV )
induced by 10kV, 15mA Al Kα radiation. Photoelectrons were collected at the take-off angle of 90°.
Cross-section TEM specimen preparation
Figure 1. A systematic diagram showing the layout of dual beam FIB system
The transfer of the specimen from the sample holder to a carbon-coated TEM grid was made ex situ using
the electrostatic force of a glass needle attached to a piezoelectric device and monitored by an optical
microscope. The novelty of this method is that it allows the preparation of cross-sectional TEM specimens
from localized regions without destruction.
Figure 2. Localizing an area of interest and producing a cross-section foil for TEM analysis
Experimental Methods (continue)
Results and discussion --- X-ray Photoelectron Spectrometry (XPS) - wide scan
Fresh
CL biochar
Aged
CL bicoar
Fresh
Saligna biochar
BMC
C 55.5 40.0 73.4 33.5
N 2.8 4.1 0.9 2.4
O 28.4 42.4 21.6 43.6
Na 0.5 - 0.3 0.4
Mg - - - 0.6
Al 0.3 7.0 - 5.0
Si 0.9 5.3 - 10.8
P 3.1 - - 0.7
S - 0.1 - 0.4
Cl 0.7 - - -
K 3.3 - 0.7 0.7
Ca 4.5 0.6 1.3 1.0
Mn - - - 0.4
Fe - 0.4 1.8 0.5
Table 1 Chemical composition (at%±1%) of the biochar surfaces as determined by XPS
After the field trial, on the aged CL biochar surface, the elemental content of O, N, Al/Si, and Fe increased. Meanwhile, Na, P, Cl,
K, and Ca decreased or could not be detected.
For Saligna biochar, after mixed with clay and minerals and thermal treatment, clay and minerals attached to the saligna biochar
surface. It’s noted that the surface content of Ca and Fe was decreased in respect to fresh biochar, which possibly resulted from
burying by clay and other minerals .
Results and discussion --- XPS C1s region scan and peak deconvolution
Fresh CL biochar
Aged CL biocharBMC
Fresh Saligna biochar
Binding Energy
(eV)
Structure Fresh
CL biochar
Aged
CL biochar
Saligna biochar BMC
C 1s 285.0±0.1 C-C/C-H 64.3 43.5 88.7 34.9
286.5±0.1 C-O 18.0 36.5 8.0 44.9
288.1±0.2 C=O 7.9 15.3 3.3 13.2
289.2±0.1 Carboxylic 3.6 4.7 - 7.0
290.5±0.2 Carbonate 6.2 - - -
Table 2 C 1s bonding state and its relative atomic percentage on the fresh and aged biochar surfaces as determined by XPS
Oxygen-contained functional group increased, especially C-O and C=O, indicating either biochar surface oxidation and adsorption of soil organic matter
Results and discussion --- SEM secondary electron images
The surface of aged CL biochar
The surface of biochar in BMC
Minerals attachment occurred on both the surfaces of aged biochar and BMC
Results and discussion --- Cross-sectional SEM backscattering electron
images and EDS mapping
BSE image C O P Al Si
Ca Mg Fe Ti Mn Al Si Ti Mn Fe
BSE image C O P Al Si
K Ca Mg Fe Ti Mn
BMC
Aged CL biochar
Except Al and Si, P, K, Ca, Mg and Fe are present in the mineral phases next to the biochar surface
Results and discussion --- cross-sectional TEM bright field images
Aged CL biochar BMC
minerals
mineralsminerals
biochar
minerals
minerals
minerals
minerals
minerals
minerals
biochar
minerals
minerals
mineralsbiochar
Minerals attachment occurred at the biochar surface.
The microstructure and composition of surrounding mineral phases are different from each other.
Results and discussion --- STEM-EDS Line scan
Aged CL biochar
interface500nm
Aluminum rich interface was discerned, possibly
due to Al-rich in Ferrosol (highly weathered soil)
Results and discussion --- STEM-EDS points analysis
BMC
EDS microanalysis
indicated that:
The interface between
biochar and mineral
phases (Point2) is rich
in P, Mg, K, Ca and Mn,
which contributed to
the incorporation of
minerals to the biocahr.
Except carboxylic and
phenols groups,
phosphate group
would provide another
reaction site produced
by H3PO4 treatment.
Conclusion
Analysis of CL biochar, recovered from the soil, showed that soil mineral
incorporation on to the biochar surfaces happened in the first year. The attachment
was localized, which indicated incorporation/adsorption of soil minerals onto
biochar surfaces was at some specific sites. Relatively high concentrations of Al
were found at the interface between biochar and mineral phases, indicating the
binding role of Al, which possibly because of the formation of carboxylic and
phenolic function groups on aged CL biochar surface by oxidation reactions.
On the other hand, H3PO4 treatment following with thermal treatment of biochar
with clay and minerals also prompt the incorporation of biochar with clay and
minerals. Multiple valence cation plays an important role in the complex process.
It is also implied that the complex is a competitive process of various cations with
activated sites, such as carboxylic group, phenolic group, and phosphate group.
Acknowledgement
Best Energies for the supply of the biochar
The Australian Microscopy and Microscopy Research Facility (AMMRF)
for access to electron microscopy and dual beam FIB.
Thanks for your attention