Engineered adsorptive materials for water remediation - Development, characterization, and application

Engineering alternative eco-friendly techniques for water remediation is a global aim due to the serious contaminations of water sources and strict standards of water quality. Engineered polymer-based adsorptive materials have emerged as new alternatives to activated carbon. Engineered adsorptive materials with embedded inorganic constituent(s) in polymeric matrix provide an opportunity to remove a diverse range of contaminants. Combining the advantages of inorganic and polymeric materials, these engineered materials exhibit enhanced properties e.g., porous structure and easy separation. Particularly, engineered adsorptive materials containing nano-sized titanium dioxide (n.TiO2) exert simultaneous adsorption and photocatalysis. These newly raised materials are new alternatives with a bright prospect in environmental remediation. This dissertation introduces new-engineered adsorptive materials for water remediation. It highlights the fundamental challenges of engineering adsorptive materials from well-known initial materials, chitosan, n.TiO2, and feldspar, for the remediation of water polluted with arsenic, Acid Black 1 dye, and phosphate in laboratory-scale. It focuses on preparing the engineered adsorptive materials, charactering them via common methods e.g., Fourier Transform Infrared Spectroscopy and X-ray Diffraction, and applying them for adsorptive (photoactive) removal of the target pollutants. The adsorption process is explored via kinetic, isotherm, and thermodynamic studies. The adsorptive materials are engineered considering the strengths and drawbacks of initial materials; e.g., n.TiO2 provides high surface area and photo-oxidation, chitosan supplies support matrix and gravity separation, and feldspar lowers the cost and improves the surface texture. The engineered materials showed improved structures and removal performances. The study of material properties revealed their functional groups, compositions, and porosity. The engineered materials embedding n.TiO2 showed enhanced UV-assisted adsorption of the dye and arsenic. UV irradiation enhanced the removal from 33% to 73% for arsenate (5 mg/L), from 23% to 84% for arsenite (5 mg/L), and from 86% to 97% for the dye (50 mg/L). Zinc-functionalized chitosan showed an improved phosphate uptake from 1.45 to 6.55 mg/g compared with plain chitosan. Adsorption kinetics indicated fast removal rates. Modeling of adsorption isotherm and kinetics via theoretical models provided fundamental information about the adsorptive surface properties and adsorption reactions. The adsorption reactions were thermodynamically spontaneous and favorable. The correspondence between the theory behind the models and properties of the engineered materials along with removal mechanisms are discussed. This dissertation provides fundamental knowledge e.g., in designing water treatment units. In summation, the experimental data and theoretical considerations support the applicability of the engineered adsorptive materials for water remediation.  

Bio-based activated carbon from husk- and wood-based biomass: comparison of carbon activation methods on organic pollutants removal

This study aimed to investigate the effect of different activations on the properties of bio-based activated carbons (BACs) for water treatment. BACs were produced via pyrolysis by the carbonization stage and were followed by four different activation procedures. Chemical activation included the introduction of metal oxides or alkali on the structure of the sawdust-derived BACs, resulting in iron-activated carbon (BAC-Fe), copper-activated carbon (BAC-Cu), and sodium-activated carbon (BAC-Na). The physical activation was conducted in a CO2 environment with the usage of two types of locally available biomasses, resulting in husk-activated carbon (HAC) and wood-activated carbon (WAC). Depending on the activation, BACs can be developed with high porosity, active sites, and different additional functionalities such as antimicrobial and magnetic. The adsorption of natural organic matter (NOM) with chemically activated BACs yielded high removal percentages (97, 87, and 80% for BAC-Fe, BAC-Cu, and BAC-Na, respectively). The physically activated BACs demonstrated high adsorption capacities for dye – 278 mg/g for WAC and 213 mg/g for HAC. This outlines a wide range of BAC production possibilities with advanced functionalities. HIGHLIGHTS Various production parameters and methods allow the modification of final properties of bio-based activated carbons.; Physical activation provides sufficient surface area for pollutants such as dye; it is cheap and environmental friendly.; Chemical activation allows the implementation of functional groups on carbon surfaces to improve adsorbent selectivity and reach specific properties.

Production and characterization of porous magnetic biochar : before and after phosphate adsorption insights

Funding Information: Open Access funding provided by Aalto University. This research was funded by Aalto University Doctoral Programme for Engineering (D/23/00.01.02.00/2019), Maa ja vesitekniikan tuki ry (Grant 388823), and the Academy of Finland (343192). Publisher Copyright: © 2022, The Author(s).The modification process of biochars enables different advantages including enhanced adsorption properties for different pollutants. Herein, porous magnetic biochars (PMB) were successfully produced from softwood biomass through a two-step pyrolysis process together with FeCl3 modification. The effect of production temperature on adsorption was studied at 200 or 300 °C, followed by iron salt modification and subsequent pyrolysis at 600 or 800 °C. Biochars were characterized before and after phosphate adsorption via various characterization methods to acquire structural, elemental, and morphological properties of the adsorbent. The effects of phosphate concentration, contact time, and temperature on the adsorption process were examined in the batch mode. The characterization showed embedded iron oxide crystals of 23 nm within the biochar structure with a magnetic strength of 38.9 emu/g, which can assist the separation process of the powdered adsorbent from the aqueous medium. The surface area of the PMB was measured as 93 m2/g and 0.002 cm3/g pore volume. PMB showed complete removal (100%) of phosphate at the lower concentration (5 mg/l P). At higher concentration (25 mg/l P), the biochar prepared under 200/800 °C showed the highest removal (30%). The adsorption was enhanced with time (optimal 3 h) and temperature, which shows endothermic chemisorption following Langmuir isotherm and Pseudo-second order kinetic models. The desorption study suggested the slow release of phosphate from the spent adsorbent and potential reuse for soil enhancement. These results point towards the sustainable use of PMB as an effective and magnetically recyclable adsorbent for phosphate removal and reclaim.Peer reviewe

Thermal conductivity of sugar alcohols

Funding Information: This work was supported by Future Makers 2019 Program (funded by Technology Industries of Finland Centennial Foundation and Jane and Aatos Erkko Foundation ), Business Finland (HeatStock project), Maj and Tor Nessling Foundation ( 201900332 ) and Academy of Finland ( 343192 ). The research made use of OtaNano Nanomicroscopy Center (NMC). The authors wish to thank also M. Sc. Markus Laitinen and B.Sc. Šimon Jech for collecting literature data. Publisher Copyright: © 2022 The AuthorsDuring the past decade sugar alcohols have been extensively studied for thermal storage purposes. One of the recent focuses of research has been in improving their heat charge and discharge rate by enhancing the thermal conductivity with different types of additives. However, the current literature shows a vast discrepancy in measured values of sugar alcohols. This work presents an experimental study on thermal conductivity of seven sugar alcohols. The aim is to find out the reason for the discrepancy of literature values for erythritol, mannitol and xylitol, and to present new reference data for galacticol, myo-inositol, maltitol and sorbitol. We study the impact of material preparation method, raw material grade and sensor contact on the crystalline structure and the conductivity. The crystalline structure was inspected with optical and scanning electron microscopy and X-ray diffraction, and melting properties with differential scanning calorimetry. We found that different polymorphs, grain structure and crystallite sizes can be obtained by different preparation methods. This caused the conductivity of mannitol, galacticol and myo-inositol to vary by tens of percentages. Crystallization temperatures of xylitol and erythritol were found to affect their grain size but had only a minor effect on the conductivity. Overall, the conductivities of solid phase sugar alcohols were found to be within the upper range of the previous literature; based on the methods of this work, we did not find any evidence for the low and intermediate values for erythritol, xylitol and mannitol. Due to the high amorphous content of maltitol and sorbitol their conductivity was substantially lower than that of the other sugar alcohols. Thermal conductivity of liquid phases was found to accurately follow a linear relationship with the molar mass for sugar alcohols with carbon number between 4 and 6.Peer reviewe

Wet Extractive Grinding Process for Efficient Calcium Recovery from Steelmaking Slags

This paper presents a process improvement of the pH-swing process (referred to as X2PCC) wherein a steelmaking slag is used as a source of calcium oxide for the mineral carbonation of CO2. We first dissolve Ca from the slag, then separate the solid phase by filtering, and, finally, bubble CO2 into the Ca-rich solution to precipitate it as CaCO3. The yield of calcium in the extraction step partly limits the process feasibility. Our objective is to apply a new extractive grinding method to enhance the extraction of Ca from steelmaking slags. We compared three cases: 1) mechanical mixing extraction with original grind slag A (0–250 μm); 2) mechanical mixing extraction with fine dry-grind slag B (0–50 μm); and 3) the new extractive wet grinding process with original slag A (0–250 μm). In this new extractive process, we combine the grinding and extraction steps in order to increase the rate and yield of the process. This method significantly reduces the energy requirement which makes this process feasible for industrial application.Peer reviewe

Tailoring metal-impregnated biochars for selective removal of natural organic matter and dissolved phosphorus from the aqueous phase

Funding Information: This work was supported by the Aalto University [Grant number D/23/00.01.02.00/2019] and Maa ja vesitekniikan tuki ry [Grant number 388823]. Publisher Copyright: © 2021 The AuthorsThis study aimed to investigate how the production process of metal impregnated biochars (MIBs) affects their selectivity in the simultaneous adsorption of organic matter and dissolved phosphorus from the aqueous phase. MIBs were produced via a two-step pyrolysis procedure including impregnation of metal oxides in the structure of the softwood-derived biochars, resulting in copper-impregnated biochar (Cu-MIB) and iron-impregnated biochar (Fe-MIB). The tailoring process was conducted by optimization of pyrolysis temperature during the biochars production stage. The MIBs were characterized via advanced characterization analyses to acquire structural, elemental, and morphological properties of the adsorbent. The surface area of MIB (99 m2/g and 92 m2/g for Cu-MIB and Fe-MIB respectively) decreased compared to pristine biochar (571 m2/g), indicating a successful impregnation of metal oxide particles within the porous carbon structure. The effect of operational parameters on adsorption as well as selectivity testswere examined in the batch mode. The optimum doses for NOM removal were 2 g/l for Fe-MIB (96%) and 0.5 g/l for Cu-MIB (87%). For phosphorus removal, optimum doses were 1 g/l for Fe-MIB (95%) and 2 g/l for Cu-MIB (93%). The lower pH values favored adsorption for both MIBs. In the binary solution of NOM and phosphorus, the NOM was selectively adsorbed by the Cu-MIB, whereas phosphorus was selectively removed by the Fe-MIB. The results provide a deeper understanding of the tailoring process of biochars for producing new biochars as selective adsorbents for specific target pollutants.Peer reviewe

Simultaneous effect of biochar-additive and lightweight heat exchanger on phase change material for low-grade thermal energy storage

Funding Information: This work was financially supported by the Academy of Finland (343192) and Business Finland (Dnro 1558/31/2019). The authors thank Kari Saari for the assistance with the system set-up and Kirsi Kukko for the 3D-printing design of the heat exchanger. The conceptualization visualization was made by the Design Factory Team in Aalto University. Funding Information: This work was financially supported by the Academy of Finland (343192) and Business Finland (Dnro 1558/31/2019). The authors thank Kari Saari for the assistance with the system set-up and Kirsi Kukko for the 3D-printing design of the heat exchanger. The conceptualization visualization was made by the Design Factory Team in Aalto University. Publisher Copyright: © 2022 The Author(s)In this paper, we report the experimental performance of a low to medium temperature (20–50 °C) latent heat heat storage (LHS) system. The power and temperature ranges of the LHS have relevance to various applications such as heat sink and storage for high-power electronics devices and low-temperature district heating (LTDH). This new LHS includes a lightweight heat exchanger (LHE) with a complex heat transfer area for organic phase change materials (PCMs). The model PCMs provide a medium-low phase transition temperature range, namely decanoic acid (DA) and a commercial PCM. To facilitate the storage performance of the system, biochar (BC) additive is further investigated to simultaneously enhance the thermal properties of the PCM within the LHE. The PCMs are characterized using common material characterization methods such differential scanning calorimetry, X-ray diffraction, and scanning electron microscopy. The system investigation focuses on the effect of the heat exchanger, the PCM type and the additive concentration on the duration and power of charging-discharging cycle as well as the storage capacity. Two weight percentages (1 % and 2 %) of BC were studied, while the addition of 1 % BC to DA resulted in the most effective storage performance in both the system (444 kJ storage capacity) and characterization (170.5 kJ/kg melting enthalpy) experiments. The lightweight structure of the grid enabled loading of a large PCM amount (1.84 kg) as well as swift charging (430 W during 25 min). The system indicated a cooperative enhancement with BC additive as the charging power increased by 32 % (570 W) and charging time decreased by 33 % (17 min). A conceptual modular design of the investigated system is proposed to heat up the floor or the bench of a smart city bus stop. The modular unit of ten integrated LHEs filled with BC enhanced DA is estimated to provide 1.2 kWh storage capacity sufficient for heating the bus floor for 6 h or the bus bench for 15 h. This is a potential solution for reclaiming the excess heat from LTDH substations, while buffering their undesired temperature variations.Peer reviewe

Ionic Mixture of Binary Sugar Alcohols and a Polymer : Composition Optimization for Long-Term Thermal Energy Storage

Funding Information: This research was supported by the Academy of Finland (343192), Business Finland (HeatStock project), and Technology Industries of Finland Centennial Foundation and Jane and Aatos Erkko Foundation (Future Makers 2019 Program). The research used characterization equipment in OtaNano Nanomicroscopy Center (NMC). The authors wish to acknowledge M.Sc. Irina Annenkova for her contribution in DSC measurements and material preparation. Publisher Copyright: © 2022 The Authors. Published by American Chemical Society.A new cold crystallizing material (NaPP) is analyzed for long-term thermal energy storage (TES). NaPP comprises a mixture of erythritol and mannitol as the binary phase change material (PCM) in the scaffold of polyvinyl alcohol (PVA) cross-linked with sodium citrate (SC). The material demonstrates a unique behavior of stable supercooling and vitrification during cooling and cold crystallization during subsequent heating, which enables a reliable long-term storage of the melting enthalpy and a controllable heat release. The use of several components in the material composition, however, impedes optimization of the thermal properties for the storage. As such, differential scanning calorimetry (DSC) was applied to expose the effect of the material components on the thermal properties, and the mixture experimental methodology (MEM) was used to model and optimize these properties. Successful modeling yielded a linear response for the thermal performance, which was significantly affected by the content of SC. Increasing the amount of SC (from 0 to 18 wt %) elevated the ionic strength of the system, which caused reduction in the amount of active PCM (confirmed by X-ray diffraction and DSC) and coarsening of the surface morphology (revealed by optical and scanning electron microscopies). This was also manifested as gradual disappearance of cold crystallization which limits the use of the material to compositions with the glass-transition temperature below -15 °C. MEM identified the optimal composition as 88.9 wt % PCM and 11.1 wt % SC, which showed a melting enthalpy of 194 J/g at 105 °C. Yet, the composition comprising 80 wt % PCM, 10 wt % PVA, and 10 wt % SC showed both high melting enthalpy (176 J/g) and shape stability facilitating larger scale applications. These compositions demonstrated a temperature increase of 10-20 °C during cold crystallization of a 10 g sample, confirming the suitability of the optimization model and the operation of the new material for long-term TES.Peer reviewe

Cost-effective Electro-Thermal Energy Storage to balance small scale renewable energy systems

Funding Information: The research received funding from the Finnish Science Foundation for Technology and Economics KAUTE s??ti? (20200551) and the Academy of Finland funding through Grant 326346 for profiling funding. The authors wish to acknowledge Kari Saari, a senior engineer at Aalto University, for validating the scientific calculations. Funding Information: The research received funding from the Finnish Science Foundation for Technology and Economics KAUTE säätiö (20200551) and the Academy of Finland funding through Grant 326346 for profiling funding. The authors wish to acknowledge Kari Saari, a senior engineer at Aalto University, for validating the scientific calculations. Publisher Copyright: © 2021 The Author(s)To decarbonise the energy production system, the share of renewable energy must increase. Particularly for small-scale stand-alone renewable energy systems, energy storage has become essential in providing electricity when the demand is high, for example, during the night. Although there are many different storage technologies, only a few are suitable for small-scale stand-alone renewable systems. Those systems must be modular and scalable to be deployed according to the capacity needed. Currently, batteries are among the leading grid storage technologies, but the demand, particularly for Lithium-ion batteries, is also high because of the electrification needs of the transportation sector. Therefore, the question of material availability might become an issue in the future, as Lithium is a scarce and critical element. As an alternative, we introduce a new modular electro-thermal energy storage (ETES) technology that is suitable for various storage needs. This storage unit can utilise various thermal storage materials (thermal oil, molten salt, and sand) at high capacities and improved efficiencies. Our design consists of the embedment of Stirling engines and an electric heater into a thermally insulated storage tank. The source electricity is first converted to heat stored in the storage tank and then converted back to electricity when needed. Among the thermal energy storage materials studied here, sand enabled the storage system's efficiency to reach 85% thanks to its wide range of operating temperatures. The cost is projected to be up to six times lower than that of current Lithium-ion batteries. This new electro-thermal energy storage provides a promising cost-efficient, high capacity alternative for stand-alone energy systems.Peer reviewe

Chitosan–Zinc(II) Complexes as a Bio-Sorbent for the Adsorptive Abatement of Phosphate: Mechanism of Complexation and Assessment of Adsorption Performance

This study examines zinc(II)–chitosan complexes as a bio-sorbent for phosphate removal from aqueous solutions. The bio-sorbent is prepared and is characterized via Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), and Point of Zero Charge (pHPZC)–drift method. The adsorption capacity of zinc(II)–chitosan bio-sorbent is compared with those of chitosan and ZnO–chitosan and nano-ZnO–chitosan composites. The effect of operational parameters including pH, temperature, and competing ions are explored via adsorption batch mode. A rapid phosphate uptake is observed within the first three hours of contact time. Phosphate removal by zinc(II)–chitosan is favored when the surface charge of bio-sorbent is positive/or neutral e.g., within the pH range inferior or around its pHPZC, 7. Phosphate abatement is enhanced with decreasing temperature. The study of background ions indicates a minor effect of chloride, whereas nitrate and sulfate show competing effect with phosphate for the adsorptive sites. The adsorption kinetics is best described with the pseudo-second-order model. Sips (R2 > 0.96) and Freundlich (R2 ≥ 0.95) models suit the adsorption isotherm. The phosphate reaction with zinc(II)–chitosan is exothermic, favorable and spontaneous. The complexation of zinc(II) and chitosan along with the corresponding mechanisms of phosphate removal are presented. This study indicates the introduction of zinc(II) ions into chitosan improves its performance towards phosphate uptake from 1.45 to 6.55 mg/g and provides fundamental information for developing bio-based materials for water remediation.Peer reviewe