Electrochemically Modified Poly(dicyandiamide) Electrodes for Detecting Hydrazine in Neutral pH

A new technique for sensing nanomolar concentrations of hydrazine in water samples is reported. A screen-printed carbon electrode (SPCE) altered using an amine-azo functional group encompassing poly-(dicyandiamide) is used in this study. The modified electrode exhibits an enhanced activity toward hydrazine detection at a lower overpotential and broad linear scale between 20 nM and 1 mM, with an accurate sensitivity value of 0.1 nA mu m(-1) cm(-2). To the best of our knowledge, poly-(dicyandiamide)-modified electrodes exhibit one of the lowest limits of detection for any metal-free electrode that detects 6.7 nM (S/N = 3) of hydrazine. The method established sufficient selectivity and better recoveries. Finally, the poly-(dicyandiamide)-modified SPCE* is highly suitable for electrochemical determination of hydrazine in water samples from tap and lake

Spectroscopic characterization of lignocellulosic biomass

This thesis focuses on characterization of organic components and inorganic elements in lignocellulosic biomass. The chosen biomass models were mostly wood from conifers and straw from rhizomatous grasses but also forest-based residues and agro-based plants. X-ray fluorescence (XRF) and near infrared (NIR) spectroscopy are techniques that can potentially be incorporated in a future biorefinery concept, where characterization of the feedstock is crucial due to the heterogeneous nature of biomass. XRF spectroscopy combined with principal component analysis (PCA) was used to classify a number of different biomass materials. Moreover, partial least squares regression calibration models were developed for several ash elements and ash content with good predictive capabilities. The capability of XRF and NIR spectroscopy to measure ash content in biomass was investigated and it was concluded that XRF spectroscopy was the superior method of the two, especially for measuring contaminated material. If the two techniques were used in conjunction, it was possible to estimate the degree of contamination. In an additional study into the potential for future separation techniques, it was shown that the 2D-NIR technique is useful for classifying wood chips, as well as identifying individual wood chips with high extractive content. Synchrotron-based X-ray absorption techniques such as X-ray absorption near edge structure (XANES) and scanning transmission X-ray microscopy (STXM) based near edge X-ray absorption fine structure (NEXAFS) spectroscopy were used to study the effect of thermal treatment of lignocellulosic material at 300 to 800 °C and low O2 partial pressures. PCA modelling of Ca XANES spectra in combination with linear fitting of spectra from reference compounds mainly confirmed the results from calculated theoretical thermodynamic models. The results from STXM C 1s NEXAFS spectroscopy showed that thermal treatment up to 300 °C induced only minor change in plant cell walls and that the major decomposition of the carbon matrix occurred between 300 and 500 °C. Nanomapping of Ca by STXM revealed a size distribution of calcium crystals mainly within the 100 to 200 nm range, which might provide an insight into the volatile behaviour of Ca in combustion processes

Dewatering properties of pulps made from different parts of a Norway spruce (Picea abies)

A single Norway spruce tree (Picea abies) was manually fractionated into heartwood, sapwood, juvenile wood and branches. These fractions were chemically pulped, individually, in laboratory scale. The pulps were characterized and investigated in relation to dewatering behavior and sheet strength properties. An unbleached and unbeaten commercial kraft pulp from softwood fibers was used as a reference, and the fractionated pulps were within the same range in all tested properties. The fractionated pulps were then compared with each other, and fiber characteristics were used to explain differences in dewatering and strength. Heartwood pulp results in stronger and stiffer papers that are harder to dewater. Sapwood pulp gives more open network structures resulting in easy dewatering and high air permeance, although with lower strength properties compared to heartwood. Pulp from Juvenile wood gives s quite strong but brittle sheets, with efficient dewatering. Pulp from branches gives paper sheets with efficient dewatering, air permeance and relatively high elongation of break but lower strength. The results show that there is definitely potential for utilizing more parts of the trees for pulp and paper making, especially when tailoring the raw material origins after preferred paper properties

Does Mechanical Screening of Contaminated Forest Fuels Improve Ash Chemistry for Thermal Conversion?

The effect of mechanical screening of severely contaminated forest fuel chips was investigated, focusing on main ashforming elements and slagging tendency and other properties with relevance for thermal conversion. In this study, screening operations were performed according to practice on an industrial scale by combining a star screen and a supplementary windshifter in six different settings and combinations. Mechanical screening reduced the amount of ash and fine particles in the accept fraction. However, the mass losses for the different screening operations were substantial (20−50 wt %). Fuel analyses of the non-screened and the screened fuels showed that the most significant screening effect was a reduction of Si and Al, indicating an effective removal of sand and soil contaminations. However, the tested fuel’s main ash-forming element’s relative concentration did not indicate any improved combustion characteristics and ash-melting behavior. Samples of the accept fractions and non-screened material were combusted in a single-pellet thermogravimetric reactor, and the resulting ashes’ morphology and elemental composition were analyzed by scanning electron microscopy−energy dispersive X-ray spectrometry and the crystalline phases by powder X-ray diffraction. Results from both these analyses confirmed that screening operations had no, or minor, effects on the fuels’ ash chemistry and slagging tendencies, i.e., the fuels’ proneness to ash melting was not improved. However, the reduction of ash and fine particles can reduce slagging and other operational problems in smaller and more sensitive combustion units

Application of design of experiments (DoE) for optimised production of micro- and mesoporous Norway spruce bark activated carbons

In this work, Norway spruce (Picea abies (Karst) L.) bark was employed as a precursor to prepare activated carbon using zinc chloride (ZnCl2) as a chemical activator. The purpose of this study was to determine optimal activated carbon (AC) preparation variables by the response surface methodology using a Box-Behnken design (BBD) to obtain AC with high specific surface area (S-BET), mesopore surface area (S-MESO), and micropore surface area (S-MICR). Variables and levels used in the design were pyrolysis temperature (700, 800, and 900 degrees C), holding time (1, 2, and 3 h), and bark/ZnCl2 impregnation ratio (1, 1.5, and 2). The optimal conditions for achieving the highest S-BET were as follows: a pyrolysis temperature of 700 degrees C, a holding time of 1 h, and a spruce bark/ZnCl2 ratio of 1.5, which yielded an S-BET value of 1374 m(2) g(-1). For maximised mesopore area, the optimal condition was at a pyrolysis temperature of 700 degrees C, a holding time of 2 h, and a bark/ZnCl2 ratio of 2, which yielded a S-MESO area of 1311 m(2) g(-1), where mesopores (S-MESO%) comprised 97.4% of total S-BET. Correspondingly, for micropore formation, the highest micropore area was found at a pyrolysis temperature of 800 degrees C, a holding time of 3 h, and a bark/ZnCl2 ratio of 2, corresponding to 1117 m(2) g(-1), with 94.3% of the total S-BET consisting of micropores (S-MICRO%). The bark/ZnCl2 ratio and pyrolysis temperature had the strongest impact on the S-BET, while the interaction between temperature and bark/ZnCl2 ratio was the most significant factor for S-MESO. For the S-MICRO, holding time was the most important factor. In general, the spruce bark AC showed predominantly mesoporous structures. All activated carbons had high carbon and low ash contents. Chemical characterisation indicated that the ACs presented disordered carbon structures with oxygen functional groups on the ACs' surfaces. Well-developed porosity and a large surface area combined with favourable chemical composition render the activated carbons from Norway spruce bark with interesting physicochemical properties. The ACs were successfully tested to adsorb sodium diclofenac from aqueous solutions showing to be attractive products to use as adsorbents to tackle polluted waters

Using macromolecular composition to predict optimal process settings in ring-die biomass pellet production

This study was performed to investigate if the process settings that give high pellet durability can be modelled from the biomass’ macromolecular composition. Process and chemical analysis data was obtained from a previous pilot-scale study of six biomass assortments that by Principal Component Analysis (PCA) was confirmed as representative for their biomass types: hardwood, softwood bark, short rotation coppice (SRC), and straw and energy crops. Orthogonal Partial Least Squares Projections to Latent Structures (OPLS) models were created with the content of macromolecules as factors and the die compression ratio and the feedstock moisture content at which the highest pellet durability was obtained as responses. The models for die compression ratio (R2X = 0.90 and Q2 = 0.58) and feedstock moisture content (R2X = 0.87 and Q2 = 0.60), rendered a prediction error for obtained mechanical durability of approximately ±1%-unit, each. Important factors for modelling of the die compression ratio were: soluble lignin (negative), acetyl groups (negative), acetone extractives (positive), and arabinan (positive). For modelling of the feedstock moisture content, Klason lignin (negative), xylan (positive), water-soluble extractives (negative), and mannan (negative), were the most influential. Results obtained in this study indicate that it is possible to predict optimal process conditions in pelletizing based on the macromolecular composition of the raw material. In practice, this would mean a higher raw material flexibility in the pellet factories through drastically reduced risk when introducing new raw materials

Facile Synthesis of Sustainable Activated Biochars with Different Pore Structures as Efficient Additive-Carbon-Free Anodes for Lithium- and Sodium-Ion Batteries

The present work elucidates facile one-pot synthesis from biomass forestry waste (Norway spruce bark) and its chemical activation yielding high specific surface area (SBET) biochars as efficient lithium-and sodium-ion storage anodes. The chemically activated biochar using ZnCl2 (Biochar-1) produced a highly mesoporous carbon containing 96.1% mesopores in its structure as compared to only 56.1% mesoporosity from KOH-activated biochars (Biochar-2). The latter exhibited a lower degree of graphitization with disordered and defective carbon structures, while the former presented more formation of ordered graphite sheets in its structure as analyzed from Raman spectra. In addition, both biochars presented a high degree of functionalities on their surfaces but Biochar-1 presented a pyridinic-nitrogen group, which helps improve its electrochemical response. When tested electrochemically, Biochar-1 showed an excellent rate capability and the longest capacity retentions of 370 mA h g-1 at 100 mA g-1 (100 cycles), 332.4 mA h g-1 at 500 mA g-1 (1000 cycles), and 319 mA h g-1 at 1000 mA g-1 after 5000 cycles, rendering as an alternative biomass anode for lithium-ion batteries (LIBs). Moreover, as a negative electrode in sodium-ion batteries, Biochar-1 delivered discharge capacities of 147.7 mA h g-1 at 50 mA g-1 (140 cycles) and 126 mA h g-1 at 100 mA g-1 after 440 cycles

Facile Synthesis of Sustainable Biomass-Derived Porous Biochars as Promising Electrode Materials for High-Performance Supercapacitor Applications

Preparing sustainable and highly efficient biochars as electrodes remains a challenge for building green energy storage devices. In this study, efficient carbon electrodes for supercapacitors were prepared via a facile and sustainable single-step pyrolysis method using spruce bark as a biomass precursor. Herein, biochars activated by KOH and ZnCl2 are explored as templates to be applied to prepare electrodes for supercapacitors. The physical and chemical properties of biochars for application as supercapacitors electrodes were strongly affected by factors such as the nature of the activators and the meso/microporosity, which is a critical condition that affects the internal resistance and diffusive conditions for the charge accumulation process in a real supercapacitor. Results confirmed a lower internal resistance and higher phase angle for devices prepared with ZnCl2 in association with a higher mesoporosity degree and distribution of Zn residues into the matrix. The ZnCl2-activated biochar electrodes' areal capacitance reached values of 342 mF cm(-2) due to the interaction of electrical double-layer capacitance/pseudocapacitance mechanisms in a matrix that favors hydrophilic interactions and the permeation of electrolytes into the pores. The results obtained in this work strongly suggest that the spruce bark can be considered a high-efficiency precursor for biobased electrode preparation to be employed in SCs

Process Parameters Optimization, Characterization, and Application of KOH-Activated Norway Spruce Bark Graphitic Biochars for Efficient Azo Dye Adsorption

In this work, Norway spruce bark was used as a precursor to prepare activated biochars (BCs) via chemical activation with potassium hydroxide (KOH) as a chemical activator. A Box–Behnken design (BBD) was conducted to evaluate and identify the optimal conditions to reach high specific surface area and high mass yield of BC samples. The studied BC preparation parameters and their levels were as follows: pyrolysis temperature (700, 800, and 900 °C), holding time (1, 2, and 3 h), and ratio of the biomass: chemical activator of 1: 1, 1.5, and 2. The planned BBD yielded BC with extremely high SSA values, up to 2209 m2·g−1. In addition, the BCs were physiochemically characterized, and the results indicated that the BCs exhibited disordered carbon structures and presented a high quantity of O-bearing functional groups on their surfaces, which might improve their adsorption performance towards organic pollutant removal. The BC with the highest SSA value was then employed as an adsorbent to remove Evans blue dye (EB) and colorful effluents. The kinetic study followed a general-order (GO) model, as the most suitable model to describe the experimental data, while the Redlich–Peterson model fitted the equilibrium data better. The EB adsorption capacity was 396.1 mg·g−1. The employment of the BC in the treatment of synthetic effluents, with several dyes and other organic and inorganic compounds, returned a high percentage of removal degree up to 87.7%. Desorption and cyclability tests showed that the biochar can be efficiently regenerated, maintaining an adsorption capacity of 75% after 4 adsorption–desorption cycles. The results of this work pointed out that Norway spruce bark indeed is a promising precursor for producing biochars with very promising properties