Abstract
Platinum group metals (PGMs), namely, Ru, Rh, and Pd, were removed simultaneously from molten borosilicate glass containing simulated high-level waste (HLW), using Sn as the solvent metal. ...The metal and glass phases were separated from each other after the melting was completed. The metal and glass phases were examined using X-ray diffraction and scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis; the composition of alloy phase was analyzed using inductively coupled plasma optical emission spectroscopy (ICP-OES). The percentage of recovery of the metal phase was 80%–87%. The metallic tin phase was found to contain PdSn4, Ru2Sn3, Ru3Sn7, and Pd0.15Rh0.15Ru0.70 intermetallic compounds, which crystallize in orthorhombic, tetragonal, cubic, and hexagonal structures, respectively. On dissolving the alloy in aqua regia, Ru3Sn7 and Pd0.15Rh0.15Ru0.70 were found to remain as an insoluble residue. The insoluble character of Ru3Sn7 and Pd0.15Rh0.15Ru0.70 affects the material balance of each element in the glass and metal alloy phases. The PGMs were separated to the metal alloy phase along with significant quantities of Fe, Te, Ni, and Mo, leaving behind Cs, Sr, and Zr in the glass phase. The recovery of PGMs has dual benefits; the removal of PGMs facilitates smooth vitrification of the waste by Joule heating. The other benefit is that of recycling PGMs (which are rare precious metals) from the waste.
Calcium phosphate glasses (CPG) with varying concentrations of uranium were synthesized by melt quench method. Maximum solid solubility of uranium in CPG was determined by using X-ray diffraction ...technique. Heat capacity (
C
p
) of the pristine CPG and uranium-loaded CPG was measured by drop calorimetry and differential scanning calorimetry. Heat capacity measured by drop calorimetry of pristine glass (CPG) was found to be 0.74 Jg
−1
K
−1
at 298 K; on loading 0.8 mol% of uranium oxide,
C
p
value decreased to 0.58 Jg
−1
K
−1
and further higher loading of 2 mol% uranium oxide shows further reduction of
C
p
to 0.55 Jg
−1
K
−1
. This decrease in
C
p
may be due to the weakening of glass network structure as uranium loading increases into glass matrix. Ratio of the number of bridging to non-bridging oxygen is decreasing gradually on increasing the amount of uranium in glass. The same has been observed for the DSC measurement as well; where the pristine glass (CPG) has higher heat capacity values compared to CPG-0.8 and CPG-2. In case of DSC, CPG-0.8 shows slightly lower values of heat capacity compared to CPG-2, this may be due to the structural changes by which the bonding between the atoms may slightly increase while going to higher amount of waste constituents. Glass transition temperature (
T
g
) of the glass matrices has been measured and it shows gradual increase on loading uranium in glass matrix from 0.8 to 6 mol%.
Platinum group metal (PGM)-free catalysts are highly desirable for oxygen reduction reaction (ORR) in electrochemical energy conversion devices, towards large scale commercialization of this ...technology. Here, we report a facile design approach using polypyrrole (PPy) hydrogel to synthesize an efficient ORR electrocatalyst featuring atomically dispersed Mn coordinated to nitrogen on partially graphitic carbon (Mn-N-C). The Mn-N-C catalyst exhibited a half-wave potential of 0.82 V
versus
the reversible hydrogen electrode, along with a limiting current density of −4.68 mA cm
−2
. The catalyst retains 87% of its original current during a short term durability test for 50 hours. Furthermore, the electron transfer number and H
2
O
2
yield for the catalyst approach 3.85-3.95 and 7.60-2.54% respectively in the potential range 0.4-0.8 V
vs.
RHE. The simplified approach can be used for the synthesis of other M-N-C catalysts for various electrochemical applications.
A facile design approach exploiting the nitrogen rich, unique three-dimensional network structure of polypyrrole (PPy) hydrogel is developed for the synthesis of a Mn-N-C electrocatalyst for the oxygen reduction reaction (ORR).
Correction for 'A polypyrrole derived nitrogen doped porous carbon support for an atomically dispersed Mn electrocatalyst for the oxygen reduction reaction' by Sanjit Kumar Parida
et al.
,
...Sustainable Energy Fuels
, 2023,
7
, 3684-3691
https://doi.org/10.1039/D3SE00495C
.
The structural stability, equation of state, and thermal expansion behavior of nanocrystalline cubic HfO2, an ultra‐high‐temperature ceramic, have been investigated using X‐ray diffraction at extreme ...conditions of pressures and temperatures. High‐pressure studies show that the cubic structure is stable up to 26.2 GPa, while the high‐temperature studies show the stability of the cubic structure up to 600°C. The Rietveld structure refinement of the high‐pressure data reveals the progressive transition of secondary monoclinic phase to the cubic phase at higher pressures. The phase progression is accompanied by incompressibility along the b axis and a large compressibility along the c axis of the monoclinic structure. The second‐order Birch‐Murnaghan equation of state fit to the unit cell volume data yielded a bulk modulus of 242(16) GPa for the cubic structure. A linear thermal expansion value of αa(c) = 8.80(15) × 10−6°C−1 and a volume thermal expansion value of αv = 26.5(4) × 10−6°C−1 have been determined from the in situ high‐temperature X‐ray diffraction studies. The results are discussed by comparing with the high‐pressure and high‐temperature behavior of isostructural ZrO2. To the best of our knowledge, this is the first experimental report on the structural stability of cubic HfO2 at high pressures.
Neodymium‐doped glass finds application in lasers with high energy and low pulse width. In the present study, a series of Nd3+ ions (0–2 mol%)‐doped strontium borophosphate (SBP) glass samples was ...prepared through the conventional melt quench method. A broad peak in the X‐ray diffraction spectrum confirmed the formation of a single‐phase amorphous borophosphate glass. Fourier transform infrared spectra of the doped and undoped glass samples indicated the presence of borate and phosphate groups that form the anionic network. The thermal properties of the glass samples were determined from thermogravimetry/differential thermal analysis. Photoluminescence and ultraviolet–visible light techniques were used to investigate the optical properties of the as‐prepared SBP:Nd glass. The Judd–Ofelt (JO) intensity parameters Ωλ (2, 4, 6), stimulated emission cross‐section, branching ratios, and transition probabilities of the Nd3+‐doped glass were obtained through the JO analysis. Characteristic Nd3+ emission peaks were observed at 1330, 1060, and 876 nm, corresponding to the 4F3/2→4IS/2 (S = 13, 11, and 9) transitions, respectively. The suitability of SBP:Nd (0.5 mol%) glass for use in solid‐state lasers was demonstrated by its intense luminescence, high transition probability, high emission cross‐section, optical gain, and luminescence branching ratio.
Near Infrared luminescence of Neodymium in Strontium Borophosphate glass.
The structural and thermal properties of sodium niobium phosphate glass are studied to analyse its suitability for immobilizing long-lived radioactive waste from nuclear reprocessing plants. Two ...series of sodium niobium phosphate glasses such as (A)
x
Nb
2
O
5
–(50−
x
)Na
2
O–50P
2
O
5
and (B)
x
Nb
2
O
5
–(50−
x
/
2)Na
2
O–(50−
x
/
2) P
2
O
5
(
x
= 0, 10, 20, 30, 40 mol.%) are prepared by the conventional melt–quenching technique. The influence of the incremental addition of Nb
2
O
5
on the structural and thermal properties of the above two series is investigated. The FTIR and Raman spectra of these glasses revealed that the number of NbO
6
octahedral chain increases with Nb content and dominates as the major structural unit over the number of PO
4
tetrahedra unit. The glass transition temperature (
T
g
), crystallization temperature (
T
c
) and melting temperature (
T
m
) are measured by using a differential scanning calorimeter (DSC). Other thermal stability parameters such as Hruby (
K
H
), Angell (
K
A
), Saad–Poulain (
K
SP
) and Weinberg (
K
W
), the total relaxation time of transformation and fragility are evaluated and compared between different composition of glasses. For both series A and B, the glass transition temperature increases with Nb content, suggesting the formation of a larger number of P–O–Nb or Nb–O–Nb linkages compared to the PO
4
tetrahedra, resulting in a more rigid network. This is confirmed by Raman spectra which show an increase in the number of Nb–O–Nb bonds with Nb content. The major crystalline phases formed by devitrifying these glasses are identified by XRD and are found to be mainly NaPO
3
, NbOPO
4
, Na
2
Nb
6
P
4
O
26
and Na
4
Nb
8
P
4
O
32
.
Phase pure zeolite-A and zeolite-X were synthesized using coal fly ash (CFA) obtained from Indian thermal power plants by employing alkali fusion method followed by hydrothermal technique. The fusion ...of fly ash with Na2CO3 was accomplished by heating at 800 °C/2 h by maintaining fly ash to Na2CO3 ratio at 1.2. The fused mass was found to be nepheline (Na4Al4Si4O16); and on subsequent treatment of the fused mass with 3 M NaOH under hydrothermal condition transformed to zeolite-A (Na12Al12Si12O48.27H2O) and zeolite-X (Na88Al88Si104O384.194H2O). The effluent solution from zeolite-A synthesis was utilized to prepare cancrinite. The zeolites were characterized by XRD, FTIR, TG-DTA, SEM and surface area of the powders were measured by BET technique. The specific surface area of the zeolite-A and zeolite-X were found to be 58.29 ± 0.20 and 164.34 ± 5.4 m2g−1 respectively. The TG-DTA studies showed the conversion of nano-crystalline to micro-crystalline zeolites with loss of adsorbed water. The ion exchange capacities of these nano-crystalline zeolites were evaluated by using simulated nuclear waste solutions containing Cs+or Sr2+ ions. The adsorption capacity of zeolite-A was found to be 95.74 mg/g and 54.12 mg/g respectively for Sr2+ and Cs+ions. Similarly, zeolite-X shows the adsorption capacity of 93.14 mg/g and 53.14 mg/g respectively for Sr2+ and Cs+ ions.
Display omitted
•Zeolite-A & zeolite-X were synthesized from fly using Na2CO3 fusion method followed by hydrothermal reaction at 100 °C/6 h.•The fly ash was converted to zeolite-A and zeolite-X through nepheline as the intermediate phase.•Specific surface area of zeolite-A & zeolite-X measured by BET technique was 58.29 ± 0.20 and 164.34 ± 5.4 m2g−1 respectively.•The adsorption capacity of zeolite-A for Sr2+ (95.74 mg/g)is higher than Cs+ ions (54.12 mg/g).•The adsorption capacity of zeolite–X for Sr2+ (93.14 mg/g)is higher than Cs+ ions (53.14 mg/g).
Enthalpy increments (∆
H
) of alkali borosilicate glasses (BSG) with and without uranium oxide were measured by drop calorimetry. The heat capacity (
C
p
) of these two glasses was computed from a ...fitted 4-term polynomial
a
+
b
T +
c
T
2
+
d
/
T
.
C
p
values were found to be 0.80–1.00 J g
−1
K
−1
and 0.83–1.13 J g
−1
K
−1
at the temperature range of
T
= 298–723 K for BSG (GM11) and UO
3
-loaded BSG (GM12), respectively. The heat capacity of borosilicate glass (BSG) GM11 and BSG-U (GM12) was also measured by DSC method and found to be 0.90–1.32 J g
−1
K
−1
and 0.84–1.19 J g
−1
K
−1
at the temperature range
T
= 320–760 K. The results were discussed based on the experimental findings.
Combustion by-products of coal from thermal power plants cause environmental pollution; efforts are made to develop techniques and green processes that could reduce the waste volume and convert the ...waste to useful materials. Synthesis of phase pure zeolites from coal fly ash and its use as adsorbent and ion exchangers to remove Cs+ and Sr2+ from simulated nuclear waste solutions is the focus of the current study. Zeolite Na–P1, hydroxy sodalite and analcime were synthesized from fly ash obtained from an Indian thermal power plant by using hydrothermal method. Zeolite synthesis conditions were optimized by studying the effect of concentration of NaOH solution, homogenization time, hydrothermal temperature and time. The zeolite phase formation, surface morphology, thermal stability studies were carried out by XRD, SEM, TG-DTA techniques; specific surface area was determined by BET analysis. Crystalline pristine zeolite Na–P1 was prepared from fly ash on reaction with 1 M NaOH at 150 °C. Similarly, hydroxy sodalite and analcime were also synthesized from the fly ash by hydrothermal reaction with 3 M NaOH at 150 °C and 5 M NaOH at 200 °C respectively. The removal efficiencies of synthesized zeolites were investigated with aqueous simulated nuclear waste solutions containing Cs+ and Sr2+. The adsorption capacities and cation exchange capacity (CEC) of zeolite Na–P1, hydroxy sodalite and analcime for Cs+ and Sr2+ ions were demonstrated. The results show the adsorption capacity of Na–P1 for Cs+ is 39.3 mg/g and for Sr2+ is 92.48 mg/g respectively and is a better adsorbent than analcime and hydroxy sodalite.
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•NaP1, hydroxy-sodalite, analcime were prepared by single step hydrothermal process.•NaOH concentration, reaction temp. & time on synthesis of zeolites was studied.•Na–P1 was prepared from fly ash by hydrothermal reaction with 1 M NaOH at 150 °C/60 h.•Hydroxysodalite prepared with 5 M NaOH/150 °C/20 h & analcime with 3 M NaOH/200 °C/10 h.•Na–P1 shows adsorption capacities of 39.3 mg/g for Cs+ &92.48 mg/g for Sr2+ ions.
