Atypical methods for characterization of used photovoltaic panels during their pre- and Post-Thermal treatment assessment

The study presents an innovative approach to the analysis of waste silicon photovoltaic panels prior and after thermal treatment. Using laser-induced breakdown spectroscopy (LIBS), the elemental composition of multilayered panel backsheets was determined, identifying a TiO2-containing coating laminate, a polyvinylidene fluoride (PVDF) layer, and an ethylene vinyl acetate (EVA) encapsulant, while also estimating their thickness. Identifying the fluorine-containing layers allowed their selective removal and safe processing of the used panels. Thermal processing parameters such as temperature (400-550 °C), time (5 - 60 min) and orientation of the busbar relative to the heat source were optimized based on contact angle measurements and CIELAB color space analysis, techniques used to detect organic residues in recovered glass and silicone. The decomposition process was examined by thermal analysis coupled with mass spectroscopy, which revealed that there were no volatile fluorine compounds in the gases released, although fluorine was detected on the recovered glass surface by SEM - EDS examination. After the PVDF layer was removed, fluorine compounds were not found in volatile gases or on the surface of recovered inorganic materials. The study indicated that the orientation of the busbars facilitates the decomposition of organic matter. Methods for reusing recovered secondary materials were also provided, suggesting the potential applications and benefits of recycling components from silicon photovoltaic panels.

In vitro evaluation of a silane containing self-adhesive resin luting agent

OBJECTIVES

To investigate the setting characteristics, wettability and bonding capacity with a lithium disilicate ceramic of a silane containing self-adhesive resin luting agent (Panavia SA Universal-PU).

METHODS

The degree of conversion (DC %) and extent of acid neutralization (SY %) of PU were measured on dual- (DC) and self-cured (SC) specimens after 10, 30 and 60 min storage by ATR-FTIR spectroscopy, whereas the presence of silanols was traced by curve-fitting the 60 min spectra, using the silane-free analog (Panavia SA Plus-PS) as a control. The role of a dedicated adhesive (Clearfil Universal Bond Quick-CU) in assisting the early DC % in PU-SC was investigated on 10 min-stored specimens. The water contact angles on polished and HF acid-etched lithium disilicate surfaces (IPS e.max Press), were assessed before and after silanization by unset PU or a silane primer (Ultradent Silane-SL). Finally, the shear strength of PU-DC specimens bonded to the acid-etched ceramic surfaces was determined before and after SL treatment.

RESULTS

The DC % was higher in DC than SC (PU, PS; all time intervals), in PU-SC than PS-SC (30, 60 min) and in the CU assisted PU-SC group. The SY % was lower in DC than SC (PU, PS) and higher in PS-SC than PU-SC groups. Silanols were found only in unset PU and PU-DC groups. SL treatment provided higher water contact angles on polished and acid-etched ceramic surfaces and higher shear bond strength on acid-etched ceramic surfaces than PU (p < 0.05 for all comparisons).

SIGNIFICANCE

Although the degree of conversion of the silane containing luting agent was improved in the self-curing mode, especially in the adhesive assisted group, it was still inferior to light-curing. Acid-neutralization and presence of silanols were affected by the setting modes. The use of a silane primer enhanced the hydrophobicity and bond strength of the silane containing luting agent with the etched ceramic substrate.

Tuning the surface using palladium based metallosurfactant for hydrogen evolution reaction

Synthesis of a novel electrocatalyst for hydrogen evolution reaction (HER) is highly demanding for renewable energy production. This research reports the design and development of novel palladium based metallosurfactant (PdCPC(I)) that belongs to the unique class of inorganic-organic hybrid with striking structural features that are explored for the first time in the HER. The formation of the micelle, molecular orientation and surface characteristics of the metallosurfactant are calculated by conductivity and contact angle measurements. The reduction of palladium in metallomicelles during electrolysis accelerates the HER. Metallosurfactant makes the substrate hydrophilic, which in turn enhances the activity of the modified substrate. The 269 mV and 400 mV (vs RHE) overpotential is required to achieve the 10 mA cm^-2 of current density for PdCPC(I) and CPC, respectively. Tafel slope of PdCPC(I) is 57 mV dec^-1, which signifies that the reaction follows the Volmer- Heyrovsky mechanism in the presence of catalyst. The presence of the palladium in the core of the micelle is certified by ICPMS study. The present electrocatalyst also demonstrates 40 h of electrochemical durability. This work opens the doors toward the enhancement of HER, which fulfills the dreams for future energy resources.

Investigating affordable cobalt based metallosurfactant as an efficient electrocatalyst for hydrogen evolution reaction

The implementation of hydrogen evolution reaction (HER) is an essential requirement of a stable electrocatalyst that competes for the performance of noble metals (Pt, Pd), especially in acidic conditions. This research reports the design and development of affordable cobalt (Co) based metallosurfactant (CoCPC(I)) which performs under acidic medium (0.5 N H₂SO₄) for HER. Such a fabricated catalyst is able to lower the cathodic potentials efficiently and exhibits 130 mV onset potential and Tafel slope of 104 mVdec^-1 that depicts the presence of Volmer-Heyrovsky mechanism. The results of the studies confirm that our synthesized metallosurfactant forms metallomicelles on the surface of electrode and surface remains stable even after the electrochemical cycle. Further, the surfactant protects the metal centre as an active site for a longer time via forming metallo-micelles which helps to sustain activity. These outcomes reveal the efficient mass and charge transfer capability of CoCPC(I) which results in faster charge transfer kinetics. Therefore, the utilization of Co based metallosurfactant can split water easily, cost-effectively, and without using hazardous chemicals. Our demonstrated technology seems suitable for industrial applications due to features of large-scale production possibilities.

Transition temperature of poly(methyl methacrylate) determined by time-of-flight secondary ion mass spectrometry and contact angle measurements

The surface chain conformations of poly(methyl methacrylate) (PMMA) at different temperatures were extensively studied by time-of-flight secondary ion mass spectrometry (ToF-SIMS). Similar to our previous experimental studies on polystyrene (PS) and poly(2, 3, 4, 5, 6-pentafluorostyrene) (5FPS), a transition temperature (T_T) could be identified through the principal component analysis (PCA) of the ToF-SIMS spectra obtained from the PMMA samples annealed at different temperatures. Interestingly, our results show that the T_T depended on molecular weight and was about 50-60˚C below the bulk glass transition temperature (T_g) and therefore could possibly be related to the surface glass transition temperature (T_g^S). These results were confirmed by contact angle measurements. ToF-SIMS results showed higher peak intensities of several low-mass oxygen-containing positive ions, hydrocarbon positive ions and OCH₃^- negative ion at higher temperatures, which can be interpreted by a higher surface concentration of methoxy groups at the surface.

Surface properties correlate to the digestibility of hydrothermally pretreated lignocellulosic Poaceae biomass feedstocks

BACKGROUND

Understanding factors that govern lignocellulosic biomass recalcitrance is a prerequisite for designing efficient 2nd generation biorefining processes. However, the reasons and mechanisms responsible for quantitative differences in enzymatic digestibility of various biomass feedstocks in response to hydrothermal pretreatment at different severities are still not sufficiently understood.

RESULTS

Potentially important lignocellulosic feedstocks for biorefining, corn stover (Zea mays subsp. mays L.), stalks of Miscanthus × giganteus, and wheat straw (Triticum aestivum L.) were systematically hydrothermally pretreated; each at three different severities of 3.65, 3.83, and 3.97, respectively, and the enzymatic digestibility was assessed. Pretreated samples of Miscanthus × giganteus stalks were the least digestible among the biomass feedstocks producing ~24 to 66.6% lower glucose yields than the other feedstocks depending on pretreatment severity and enzyme dosage. Bulk biomass composition analyses, 2D nuclear magnetic resonance, and comprehensive microarray polymer profiling were not able to explain the observed differences in recalcitrance among the pretreated feedstocks. However, methods characterizing physical and chemical features of the biomass surfaces, specifically contact angle measurements (wettability) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy (surface biopolymer composition) produced data correlating pretreatment severity and enzymatic digestibility, and they also revealed differences that correlated to enzymatic glucose yield responses among the three different biomass types.

CONCLUSION

The study revealed that to a large extent, factors related to physico-chemical surface properties, namely surface wettability as assessed by contact angle measurements and surface content of hemicellulose, lignin, and wax as assessed by ATR-FTIR rather than bulk biomass chemical composition correlated to the recalcitrance of the tested biomass types. The data provide new insight into how hydrothermal pretreatment severity affects surface properties of key Poaceae lignocellulosic biomass and may help design new approaches to overcome biomass recalcitrance.

Effects of processing on the properties of chitosan/cellulose nanocrystal films

Biocomposites of chitosan (CS)/cellulose nanocrystals (CN) were prepared by using solution casting method. Influences of solution preparation method and CN content on the properties of composites were investigated. Mechanical stirring/ultrasonication or microfluidization were used to disperse nanocrystals in the chitosan matrix. The prepared nanocomposites were characterized by FTIR, XRD, SEM, DSC, TGA, TMA and contact angle measurements. SEM analysis revealed that microfluidization decreased CN aggregates in matrix. Formation of hydrogen bonds between CS and CN in nanocomposites prepared by using microfluidization was confirmed by FTIR spectroscopy. This high interaction led to an increment of the crystallinity of chitosan films. Tg values within a range of 53-58°C were obtained in DSC and TMA measurements. The thermal stability of CS film showed no significant effect of CN addition, whereas contact angle measurements revealed that CN addition resulted in an increment of hydrophilicity of chitosan films.