inorganic polymers
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2022 ◽  
Vol 153 ◽  
pp. 106655
Author(s):  
Roberto Murillo Alarcón ◽  
Tobias Hertel ◽  
Elise François ◽  
Hubert Rahier ◽  
Yiannis Pontikes

Materials ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 147
Author(s):  
Adrian Ionut Nicoara ◽  
Alina Ioana Badanoiu

The main objective of this study is the synthesis and characterization of low cost alkali-activated inorganic polymers based on waste glass (G-AAIPs) using a mixture of NaOH and Ca(OH)2 as alkali activators, in order to improve their hydrolytic stability. This paper also presents detailed information about the influence of composition determined by X Ray Diffraction (XRD), microstructure determined by Scanning Electronic Microscopy (SEM) and processing parameters on the main properties of G-AAIP pastes. The main factors analyzed were the glass fineness and the composition of the alkaline activators. The influence on intumescent behavior was also studied by heat treating of specimens at 600 °C and 800 °C. The use of Ca(OH)2 in the composition of the alkaline activator determines the increase of the hydrolytic stability (evaluated by underwater evolution index) of the G-AAIP materials compared to those obtained by NaOH activation. In this case, along with sodium silicate hydrates, calcium silicates hydrates (C-S-H), with good stability in a humid environment, were also formed in the hardened pastes. The highest intumescence and an improvement of hydrolytic stability (evaluated by underwater evolution index and mass loss) was achieved for the waste glass powder activated with a solution containing 70% NaOH and 30% Ca(OH)2. The increase of the waste glass fineness and initial curing temperature of G-AAIPs have a positive effect on the intumescence of resulted materials but have a reduced influence on their mechanical properties and hydrolytic stability.


2021 ◽  
Author(s):  
◽  
Mohammad Al-Zeer

<p>Recent increased environmental awareness and the stimulus of greener chemistry has driven the rapid development of heterogeneous catalysts, particularly solid acids, for a wide range of organic synthesis applications. Typical homogenous acids suffer drastic drawbacks in terms of their corrosivity, toxicity, and reusability, in addition to their separation that generates large amounts of industrial wastes which exceeds in many cases the amount of the formed products.  Crystalline aluminosilicate inorganic polymers (zeolites) have successfully replaced the typical homogenous Lewis acids in many industrially important applications, the majority of which are in the petrochemical industries, e.g. production of olefins and aromatics. The fine chemical industries, however, are more challenging and still mainly use homogenous catalysts. Typical zeolite catalysts are hindered by their restricted micropores, and the low hydrothermal stability of other mesoporous M-silicates (such as MCM-41) results in structural deformation in aqueous solutions at elevated temperatures. Other highly promising solid catalysts suffer drawbacks of high cost, sophisticated synthesis procedures, and environmental risks from the use of toxic reagents. Thus, there is still a need for new cost-efficient reactive heterogeneous solid catalysts that are also environmentally benign.  This thesis reports the development of amorphous aluminosilicate inorganic polymers (known as geopolymers) as a novel class of heterogeneous solid acid catalysts. These geopolymers can be synthesised with the desired acidity and porosity in a very energy-efficient and simple procedure which does not involve lengthy thermal treatments or the use of costly and sometimes toxic structural directing agents that are required for the synthesis of zeolite or other mesoporous aluminosilicates.  Microporous, mesoporous and hierarchical geopolymer-based catalysts were synthesised from different precursors with high surface area and acidic sites (Bronsted and Lewis) generated within their structure by ion-exchange with ammonium ions followed by thermal treatment, allowing the nature of these acidic sites to be tailored to specific applications. Furthermore, some of the resulting geopolymer catalysts were subjected to post synthetic treatments (demetallation) which provided improved acidity and porosity.  In the first instance, the geopolymer-based catalysts were synthesised from a naturally occurring clay mineral and their catalytic performance was evaluated in the industrially important Beckmann rearrangement of cyclohexanone oxime to 𝜀-caprolactam. High catalytic reactivity and selectivity was achieved over the geopolymer-based catalysts that possess high surface area and weak surface acidities consisting of H-bonded silanol nests and vicinal silanols. The catalytic reactivity of the clay-based geopolymer catalysts was further evaluated in the Friedel-Crafts alkylation of large substituted arenes with benzyl halide as alkylating agent, where typical microporous zeolites show poor reactivity due to diffusional limitations. In this reaction, the thermal treatment was adjusted to generate the required Bronsted and Lewis acidic sites. High reactivity was achieved over several mesoporous geopolymer-based catalysts, with the best performance being observed over a hierarchical geopolymer-based catalyst that exhibits the highest acidity of all these new catalysts.  In another approach, highly reactive geopolymer-based catalysts were synthesised from industrial wastes precursors (fly ash). Several fly ashes were collected from different sources and the influence of their chemical and physical properties on the resulting geopolymers was investigated. These fly ash-based catalysts demonstrated excellent catalytic performance in the alkylation of benzene and substituted benzenes and their active sites were ascribed to a combination of Fe2O3 present in the raw fly ash, together with the Bronsted and Lewis acid sites that were generated within the geopolymers framework by the ion-exchange process followed by thermal treatment.  The use of the fly ash-based catalysts was also demonstrated in another highly demanding catalytic process, the Friedel-Crafts acylation of aromatics. High reactivity and selectivity was achieved in the acylation reactions of anisole and mesitylene using benzoylchloride as the acylating agent. In addition to their excellent catalytic reactivities, the fly ash-based geopolymer catalysts provide a valuable approach of the utilisation of industrial wastes such as fly ash, the vast production of which is becoming a world-wide concern.  The geopolymer-based catalysts developed in this work are reusable without significant loss of reactivity and their catalytic performance is superior to other commonly used solid acid catalysts. The results presented in this thesis demonstrate a great potential for geopolymers as active candidates in the field of heterogeneous catalysis, representing as they do a new class of solid acids with highly desirable features such as catalytic efficiency as well as ecological friendliness, cost effectiveness and ease of synthesis.</p>


2021 ◽  
Author(s):  
◽  
Mohammad Al-Zeer

<p>Recent increased environmental awareness and the stimulus of greener chemistry has driven the rapid development of heterogeneous catalysts, particularly solid acids, for a wide range of organic synthesis applications. Typical homogenous acids suffer drastic drawbacks in terms of their corrosivity, toxicity, and reusability, in addition to their separation that generates large amounts of industrial wastes which exceeds in many cases the amount of the formed products.  Crystalline aluminosilicate inorganic polymers (zeolites) have successfully replaced the typical homogenous Lewis acids in many industrially important applications, the majority of which are in the petrochemical industries, e.g. production of olefins and aromatics. The fine chemical industries, however, are more challenging and still mainly use homogenous catalysts. Typical zeolite catalysts are hindered by their restricted micropores, and the low hydrothermal stability of other mesoporous M-silicates (such as MCM-41) results in structural deformation in aqueous solutions at elevated temperatures. Other highly promising solid catalysts suffer drawbacks of high cost, sophisticated synthesis procedures, and environmental risks from the use of toxic reagents. Thus, there is still a need for new cost-efficient reactive heterogeneous solid catalysts that are also environmentally benign.  This thesis reports the development of amorphous aluminosilicate inorganic polymers (known as geopolymers) as a novel class of heterogeneous solid acid catalysts. These geopolymers can be synthesised with the desired acidity and porosity in a very energy-efficient and simple procedure which does not involve lengthy thermal treatments or the use of costly and sometimes toxic structural directing agents that are required for the synthesis of zeolite or other mesoporous aluminosilicates.  Microporous, mesoporous and hierarchical geopolymer-based catalysts were synthesised from different precursors with high surface area and acidic sites (Bronsted and Lewis) generated within their structure by ion-exchange with ammonium ions followed by thermal treatment, allowing the nature of these acidic sites to be tailored to specific applications. Furthermore, some of the resulting geopolymer catalysts were subjected to post synthetic treatments (demetallation) which provided improved acidity and porosity.  In the first instance, the geopolymer-based catalysts were synthesised from a naturally occurring clay mineral and their catalytic performance was evaluated in the industrially important Beckmann rearrangement of cyclohexanone oxime to 𝜀-caprolactam. High catalytic reactivity and selectivity was achieved over the geopolymer-based catalysts that possess high surface area and weak surface acidities consisting of H-bonded silanol nests and vicinal silanols. The catalytic reactivity of the clay-based geopolymer catalysts was further evaluated in the Friedel-Crafts alkylation of large substituted arenes with benzyl halide as alkylating agent, where typical microporous zeolites show poor reactivity due to diffusional limitations. In this reaction, the thermal treatment was adjusted to generate the required Bronsted and Lewis acidic sites. High reactivity was achieved over several mesoporous geopolymer-based catalysts, with the best performance being observed over a hierarchical geopolymer-based catalyst that exhibits the highest acidity of all these new catalysts.  In another approach, highly reactive geopolymer-based catalysts were synthesised from industrial wastes precursors (fly ash). Several fly ashes were collected from different sources and the influence of their chemical and physical properties on the resulting geopolymers was investigated. These fly ash-based catalysts demonstrated excellent catalytic performance in the alkylation of benzene and substituted benzenes and their active sites were ascribed to a combination of Fe2O3 present in the raw fly ash, together with the Bronsted and Lewis acid sites that were generated within the geopolymers framework by the ion-exchange process followed by thermal treatment.  The use of the fly ash-based catalysts was also demonstrated in another highly demanding catalytic process, the Friedel-Crafts acylation of aromatics. High reactivity and selectivity was achieved in the acylation reactions of anisole and mesitylene using benzoylchloride as the acylating agent. In addition to their excellent catalytic reactivities, the fly ash-based geopolymer catalysts provide a valuable approach of the utilisation of industrial wastes such as fly ash, the vast production of which is becoming a world-wide concern.  The geopolymer-based catalysts developed in this work are reusable without significant loss of reactivity and their catalytic performance is superior to other commonly used solid acid catalysts. The results presented in this thesis demonstrate a great potential for geopolymers as active candidates in the field of heterogeneous catalysis, representing as they do a new class of solid acids with highly desirable features such as catalytic efficiency as well as ecological friendliness, cost effectiveness and ease of synthesis.</p>


2021 ◽  
Vol 2131 (5) ◽  
pp. 052033
Author(s):  
A Sychev ◽  
V Avilov ◽  
M Savenkova ◽  
E Luneva ◽  
A Sychev

Abstract Various problems and different approaches of solution of such a problematic unit as “centre block-footstep bearing” of freight cars are discussed in the paper. The methods of improving the tribological properties of this friction unit by means of material modification of friction surfaces and perfection of physical, chemical and tribological properties of the used lubricants were studied. Grease lubricants common for friction units of railway machinery were used after being modified with inorganic polymers based on double metaphosphates. Bench and operational tests of the developed additive of the polymeric double metaphosphates were carried out. This additive reduces wear and increases the service life of the friction unit, due to the better adhesion properties of this additive. The variants with a change in the geometry of the contact surface of the disk between the bolster and the “centre block-footstep bearing” arrangement of the car are considered. Simulation of the parameters of movement in curved sections is proposed.


2021 ◽  
Vol 5 (12) ◽  
pp. 312
Author(s):  
Ismail Luhar ◽  
Salmabanu Luhar

The discovery of an innovative class of inorganic polymers has brought forth a revolution in the history of construction technology. Now, no energy-intensive reactions at elevated temperatures are essential, as found in the case of contemporary cement production. In addition to their attributes of low energy and a mitigated carbon footprint, geopolymeric composites can incorporate diversely originated and profound wastes in their manufacturing. As of today, profoundly accessible landfills of rubber tyre waste negatively impact the environment, water, and soil, with many health hazards. Their nonbiodegradable complex chemical structure supports recycling, and toxic gases are emitted by burning them, leading to aesthetic issues. These, altogether, create great concern for well-thought-out disposal methods. One of the achievable solutions is processing this waste into alternative aggregates to thus generate increased economic value whilst reducing primary aggregate consumption through the incorporation of these vast automobile solid wastes in the manufacturing of geopolymer construction composites, e.g., binders, mortar, concrete, etc., produced through the process of geopolymerization as a replacement for natural aggregates, providing relief to the crisis of the degradation of restricted natural aggregate resources. Currently, tyre rubber is one of the most outstanding materials, extensively employed in scores of engineering applications. This manuscript presents a state-of-the-art review of value-added applications in the context of rubberized geopolymer building composites and a review of past investigations. More significantly, this paper reviews rubberized geopolymer composites for their value-added applications.


Polymers ◽  
2021 ◽  
Vol 13 (22) ◽  
pp. 3963
Author(s):  
Florin Bucatariu ◽  
Carmen Teodosiu ◽  
Irina Morosanu ◽  
Daniela Fighir ◽  
Ramona Ciobanu ◽  
...  

Advanced wastewater treatment processes are required to implement wastewater reuse in agriculture or industry, the efficient removal of targeted priority and emerging organic & inorganic pollutants being compulsory (due to their eco-toxicological and human health effects, bio-accumulative, and degradation characteristics). Various processes such as membrane separations, adsorption, advanced oxidation, filtration, disinfection may be used in combination with one or more conventional treatment stages, but technical and environmental criteria are important to assess their application. Natural and synthetic polyelectrolytes combined with some inorganic materials or other organic or inorganic polymers create new materials (composites) that are currently used in sorption of toxic pollutants. The recent developments on the synthesis and characterization of composites based on polyelectrolytes, divided according to their macroscopic shape— beads, core-shell, gels, nanofibers, membranes—are discussed, and a correlation of their actual structure and properties with the adsorption mechanisms and removal efficiencies of various pollutants in aqueous media (priority and emerging pollutants or other model pollutants) are presented.


2021 ◽  
Author(s):  
◽  
Mahroo Falah

<p>This thesis describes the development and performance of novel photocatalytic inorganic polymer (geopolymer) composites for photodegradation of environmentally harmful organic materials. Nanometer-sized cubic cuprous oxide nanoparticles and spherical Cu₂O/TiO₂ nano-heterostructures were synthesized via a precipitation method and then added to a metakaolinite-based geopolymer matrix prior to curing at ambient temperature.  The morphology of the homogeneous oxide nanoparticle dispersion within the geopolymer matrix was demonstrated by SEM/EDS and HRTEM. FTIR spectroscopy confirmed the formation of a well-reacted geopolymer matrix that was unaffected by the insertion of the Cu₂O and Cu₂O/TiO₂ nanoparticles. The structures of these new composites were determined by ²⁷Al and ²⁹Si MAS NMR spectroscopy. ⁶³Cu NQR spectroscopy and XRD confirmed that the metal oxide nanoparticles are unchanged by their incorporation in the geopolymer composite and after the photodegradation reactions. The nitrogen adsorption-desorption isotherms were determined, providing information about the specific surface areas and total pore volumes of the composites. The action of the composites in the adsorption and photocatalytic destruction of the model organic compound MB was determined under dark and UV illumination conditions. Experiments in dark conditions and under UV irradiation showed that these materials efficiently remove a model organic pollutant (MB dye) from solution by a dual process of adsorption on the geopolymer matrix, and photodecomposition of the dye without destroying the geopolymer structure. The adsorption kinetics of the dye are best described by a pseudo first-order model and the adsorption process by Langmuir-Freundlich isotherms.  In a novel extension of this research, the metakaolinite-based geopolymer matrix was modified with a surfactant (cetyltrimethylammonium bromide, CTAB), exploiting the cation exchange capacity of the geopolymers structure. The nano oxide composites were synthesised by adding different amounts of as-prepared metal oxide nanoparticles to the modified geoplymer to produce a hydrophobic photocatalyst composite with improved photocatalytic activity arising from the dispersion of the metal oxide nanoparticles in the external surfaces and interlayers of the geopolymer matrix. This method has the advantage of producing geopolymer composites with a stable pH which are more suitable for dye degradation studies.  At concentrations >20 wt%, the photo-oxide component decreases the adsorption rate by blocking the active adsorption sites of the geopolymer. Under UV radiation, the composites remove the MB by a combination of adsorption and photodegradation, without deterioration of the geopolymer structure or the photoactive metal oxide component.  In addition these studies show that the metal oxide-geopolymer nano composites have significantly improved photocatalytic activity compared with the oxide nanoparticles alone, because of the unique properties of these inorganic polymers. These results demonstrate that composites of nanosized Cu₂O particles and photoreactive TiO₂ in an aluminosilicate inorganic polymer matrix constitute new and novel materials with potential environmental protection applications to efficiently remove organic pollutants from water or the atmosphere.</p>


2021 ◽  
Author(s):  
◽  
Siti Noor Syazana Md Hairi

<p>Red mud is the highly alkaline, toxic residue of the aluminium ore bauxite after extraction of the aluminium by the Bayer process. The storage and utilization of red mud present significant environmental problems. The possibility of producing viable inorganic polymers (geopolymers) from red mud and its precursor mineral bauxite was investigated, using sodium hydroxide and/or sodium silicate as the activator, and adjusting the composition of the mixture by the addition of fine silica or ρ-alumina. The compressive strengths of the samples were measured after curing for 21 days. Although all the samples showed drying cracking, the strengths were very encouraging, the highest strength being 58 Mpa from a red mud sample containing additional silica, and the highest strength from bauxite samples being 28 MPa; the compositions of these samples also being adjusted by the addition of fine silica. These strongest samples were prepared from red mud and bauxite that had been calcined at 500°C given by RMGP4, and 28 MPa from BS2. They were made from calcined red mud and bauxite, which therefore seem to be more reactive to alkali than the as-received materials. XRD, SEM/EDS and solid-state NMR spectroscopy were used to study the microstructure and compositions of the end products. XRD revealed that iron occurs as hematite (Fe₂O₃) in the red mud, bauxite and most of the red mud geopolymers, and is present as other crystalline minerals in the other geopolymer samples. SEM spectroscopy shows that the red mud and bauxite were relatively highly porous and non-crystalline. EDS confirms that iron is present as one of the major elements in the material as well as in the geopolymers. ²⁷Al NMR spectroscopy revealed that Al is present in more tetrahedrally coordinated sites than in octahedral. ²⁹Si NMR is greatly affected by the presence of iron, resulting in very noisy spectra and in some cases no signals were obtained. These results suggest that iron does not necessarily interfere with geopolymer formation, and thus the utilisation of red mud to produce usefully strong geopolymers on a larger scale is feasible, provided the problem of cracking can be solved.</p>


2021 ◽  
Author(s):  
◽  
Mahroo Falah

<p>This thesis describes the development and performance of novel photocatalytic inorganic polymer (geopolymer) composites for photodegradation of environmentally harmful organic materials. Nanometer-sized cubic cuprous oxide nanoparticles and spherical Cu₂O/TiO₂ nano-heterostructures were synthesized via a precipitation method and then added to a metakaolinite-based geopolymer matrix prior to curing at ambient temperature.  The morphology of the homogeneous oxide nanoparticle dispersion within the geopolymer matrix was demonstrated by SEM/EDS and HRTEM. FTIR spectroscopy confirmed the formation of a well-reacted geopolymer matrix that was unaffected by the insertion of the Cu₂O and Cu₂O/TiO₂ nanoparticles. The structures of these new composites were determined by ²⁷Al and ²⁹Si MAS NMR spectroscopy. ⁶³Cu NQR spectroscopy and XRD confirmed that the metal oxide nanoparticles are unchanged by their incorporation in the geopolymer composite and after the photodegradation reactions. The nitrogen adsorption-desorption isotherms were determined, providing information about the specific surface areas and total pore volumes of the composites. The action of the composites in the adsorption and photocatalytic destruction of the model organic compound MB was determined under dark and UV illumination conditions. Experiments in dark conditions and under UV irradiation showed that these materials efficiently remove a model organic pollutant (MB dye) from solution by a dual process of adsorption on the geopolymer matrix, and photodecomposition of the dye without destroying the geopolymer structure. The adsorption kinetics of the dye are best described by a pseudo first-order model and the adsorption process by Langmuir-Freundlich isotherms.  In a novel extension of this research, the metakaolinite-based geopolymer matrix was modified with a surfactant (cetyltrimethylammonium bromide, CTAB), exploiting the cation exchange capacity of the geopolymers structure. The nano oxide composites were synthesised by adding different amounts of as-prepared metal oxide nanoparticles to the modified geoplymer to produce a hydrophobic photocatalyst composite with improved photocatalytic activity arising from the dispersion of the metal oxide nanoparticles in the external surfaces and interlayers of the geopolymer matrix. This method has the advantage of producing geopolymer composites with a stable pH which are more suitable for dye degradation studies.  At concentrations >20 wt%, the photo-oxide component decreases the adsorption rate by blocking the active adsorption sites of the geopolymer. Under UV radiation, the composites remove the MB by a combination of adsorption and photodegradation, without deterioration of the geopolymer structure or the photoactive metal oxide component.  In addition these studies show that the metal oxide-geopolymer nano composites have significantly improved photocatalytic activity compared with the oxide nanoparticles alone, because of the unique properties of these inorganic polymers. These results demonstrate that composites of nanosized Cu₂O particles and photoreactive TiO₂ in an aluminosilicate inorganic polymer matrix constitute new and novel materials with potential environmental protection applications to efficiently remove organic pollutants from water or the atmosphere.</p>


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