Search

Reducing CO2 emissions alone will not suppress global warming, and it is necessary to capture the CO2 that has been cumulatively emitted into the atmosphere as well. For this reason, negative CO2 emission technology, a technology to capture CO2 from the atmosphere, is considered essential. Especially, direct capture of CO2 from the air, so-called direct air capture (DAC) has attracted much attention as one of promising technologies, because of the high potential capacity of CO2 capture. In general, absorption, adsorption, and membrane separation are known as representative CO2 capture technologies, and DAC is basically based on these technologies. In particular, DAC using absorption and adsorption methods has already reached the level of plant scale, but the desorption process of captured CO2 from the absorbent or adsorbent consumes a large amount of heating energy and water. On the other hand, membrane separation is generally considered as a most cost- and energy-efficient process among these capture technologies, but DAC by membrane separation has not been considered at all due to the immaturity of the membrane performance for CO2 capture, especially CO2 permeance. However, recent developments in membrane technology have brought the possibility that membrane processes can be considered as a new approach to DAC. In this article, the potential of membrane technologies as DAC is discussed and future technology target is proposed. Graphical abstract

A polymer of intrinsic microporosity (PIM) consisting of Tröger's base (TB) undergoes ring opening of the bicyclic amine upon N‐methylation followed by alkaline hydrolysis, resulting in a hybrid ladder polymer that contains diazacyclooctane (DACO) units with tert‐ and sec‐amino groups. The hybrid ladder polymers with various TB/DACO ratios can be prepared depending on the reaction conditions. Here we report a systematic study on the effect of DACO content on the thermal and gas adsorption properties of the hybrid ladder polymer. Using a PIM derived from 2,5‐diamino‐p‐xylene, we prepared hybrid ladder polymers with a DACO content ranging from 19% to 55% while having a similar molecular weight. The thermal stability of the hybrid ladder polymers, evaluated by thermogravimetric analysis, is decreased with the increase in DACO content. Based on gas adsorption measurements, the increase in DACO content results in the decrease in the BET surface area but improves the gas adsorption selectivity for CO2 against N2, likely due to high basicity of the sec‐amino group of DACO unit. This result demonstrates that the partial TB‐to‐DACO conversion of the TB‐based PIM may provide a simple but useful strategy to design polymer materials that enable selective CO2 capture and/or separation.

Abstract Nanocellulose is a promising new membrane material for fuel cells, with much lower cost and environmental impact compared with Nafion or Aquivion. It is mechanically strong, is an excellent hydrogen barrier and has reasonable proton conductivity. Here, sulfonation of cellulose nanofibers is performed to enhance the conductivity (up to 2 × 10− 3 S cm− 1) without compromising the membrane integrity, and fuel cells are fabricated with 30 µm-thick “paper” membranes. The hydrogen crossover current is two orders of magnitude lower than for Nafion fuel cells with equivalent thickness, but the power density is rather low. Spray-coating is used to deposit 8 µm-thick membranes directly onto the electrocatalyst layer, in a process analogous to 3D printing or additive manufacturing. The resulting paper fuel cell has high current density (> 0.8 A cm− 2) and power density (156 mW cm− 2) under standard measurement conditions (H2/air; 80°C; 95% RH; 0.1 MPa), attributed to decreased membrane resistance. The cost of the spray-painted cellulose membranes is calculated to be ~ 50 $ m− 2, which is much lower than that of Nafion, even without taking into consideration economies of scale. This new concept in electrochemical energy conversion paves the way for the mass production of affordable, recyclable fuel cells. Graphic abstract

Natural gas, having a significantly lower CO2 emission factor than oil and coal when combusted, is accepted as an important transition fuel towards carbon net-zero society. To meet the calorific value requirements (≥34.0 MJ m−3) and reduce possible corrosion of transportation pipelines, acid gases such as CO2 and H2S must be removed from raw natural gas. Membrane separation is a promising alternative approach to remove acid gases from natural gas. This paper aims to review the development of various polymer-based membranes and membrane processes for H2S separation from natural gas. Progress in glassy polymer membranes, rubbery polymer membranes, hybrid membranes and membrane contactors for H2S removal from natural gas is summarized and analyzed. The H2S separation performance of various membranes is plotted in one diagram and a new H2S/CH4 upper bound is proposed. Challenges of membranes for H2S separation and prospects of future development are thoroughly discussed.

Direct CO2 capture from the air, so-called direct air capture (DAC), has become inevitable to reduce the concentration of CO2 in the atmosphere. Current DAC technologies consider only sorbent-based systems. Recently, there have been reports that show ultrahigh CO2 permeances in gas separation membranes and thus membrane separation could be a potential new technology for DAC in addition to sorbent-based CO2 capture. The simulation of chemical processes has been well established and is commonly used for the development and performance assessment of industrial chemical processes. These simulations offer a credible assessment of the feasibility of membrane-based DAC (m-DAC). In this paper, we discuss the potential of m-DAC considering the state-of-the-art performance of organic polymer membranes. The multistage membrane separation process was employed in process simulation to estimate the energy requirements for m-DAC. Based on the analysis, we propose the target membrane separation performance required for m-DAC with competitive energy expenses. Finally, we discuss the direction of future membrane development for DAC. Direct CO2 capture from the air (DAC), is inevitable to reduce the concentration of CO2 in the atmosphere. Recent reports of ultrahigh CO2 permeances in gas separation membranes indicate a potential of new technology for DAC (m-DAC). In this paper, we use chemical process simulation to discuss the potential of m-DAC considering the state-of-the-art performance of organic polymer membranes. Based on the analysis, we propose the target properties for separation membranes required for m-DAC with competitive energy expenses as well as the direction of future membrane development for DAC.

In this work, we deposited a CO2-selective block copolymer, Pebax-1657, as a selective layer with a thickness of 2-20 nm on the oxygen plasma-activated surface of poly(dimethylsiloxane) (PDMS) used as a gutter layer (thickness ∼400 nm). This double-layered structure was subsequently transferred onto the polyacrylonitrile (PAN) microporous support and studied for CO2/N2 separation. The effect of interfacial molecular arrangements between the selective and gutter layers on CO2 permeance and selectivity has been investigated. We have revealed that the gas permeance and selectivity do not follow the conventional theoretical predictions for the multilayer membrane (resistance in series transport model); specifically, more selective CO2/N2 separation membranes were achieved with ultrathin selective layers. Detailed characterization of the chemical structure of the outermost membrane surface suggests that nanoscale blending of the ultrathin Pebax-1657 layer with O2 plasma-activated PDMS chains on the surface takes place. This nanoblending at the interface between the selective and gutter layers played a critical role in enhancing the CO2/N2 selectivity. CO2 permeances in the developed thin-film composite membranes (TFCM) were between 1200 and 3500 gas permeance units (GPU) and the respective CO2/N2 selectivities were between 72 and 23, providing the gas separation performance suitable for CO2 capture in postcombustion processes. This interpenetrating polymer interface enhanced the overall selectivity of the membrane significantly, exceeding the separation ability of the pristine Pebax-1657 polymer.

Fabrication and gas permselective behavior of free-standing polydimethylsiloxane (PDMS) nanomembranes are discussed. The largest CO2 permeance is close to 40,000 GPU (the highest one ever reported)...

Inorganic–organic nanocomposite hybrids containing zirconium dioxide (ZrO2) as inorganic cross-linker/filler and polydimethylsiloxane (PDMS) as a polymeric matrix have been synthesized using the in...

The unique frictional behavior of polyethylenimine/molybdenum disulphide (PEI/MoS2)n thin films on steel substrates, deposited via the layer-by-layer (LbL) technique, is explored. The effects of gaseous atmosphere (i.e. air vs. dry nitrogen), and heat treatment of the coatings are investigated. The coefficients of friction (COFs) are reduced by factors of ca. 2 and 11 in air and N2 respectively, compared to an uncoated steel substrate. Ultra-low friction (COF

Highly sensitive fiber-optic ammonia gas sensors were fabricated via layer-by-layer deposition of poly(diallyldimethylammonium chloride) (PDDA) and tetrakis(4-sulfophenyl)porphine (TSPP) onto the surface of the core of a hard-clad multimode fiber that was stripped of its polymer cladding. The effects of film thickness, length of sensing area, and depth of evanescent wave penetration were investigated to clearly understand the sensor performance. The sensitivity of the fiber-optic sensor to ammonia was linear in the concentration range of 0.5–50 ppm and the response and recovery times were less than 3 min, with a limit of detection of 0.5 ppm, when a ten-cycle PDDA/TSPP film was assembled on the surface of the core along a 1 cm-long stripped section of the fiber. The sensor’s response towards ammonia was also checked under different relative humidity conditions and a simple statistical data treatment approach, principal component analysis, demonstrated the feasibility of ammonia sensing in environmental relative humidity ranging from dry 7% to highly saturated 80%. Penetration depths of the evanescent wave for the optimal sensor configuration were estimated to be 30 and 33 nm at wavelengths of 420 and 706 nm, which are in a good agreement with the thickness of the 10-cycle deposited film (ca. 30 nm).

We have prepared new charge-transfer (CT) complex polymer blend membranes (CT membranes), for use as high performance polymer electrolyte membranes (PEMs); with a simple and easy preparation method for application in PEFCs. In this study, electron-accepting sulfonated polyimide (SPI) and electron-donating polyether (PE), were used to develop polymer-polymer type CT membranes. The formation of CT complex in the obtained SPI/PE membranes was confirmed by visible spectroscopy. The use of flexible spacers in the PE and heat treatment of the CT membranes, enhanced the CT complex formation. SPI/PE CT membranes showed 1.9–2.2 times higher mechanical strength than the original SPI, while SPI/PE 0.33 CT membrane with heat treatment at 130 °C for 2 h showed 4.3 times higher mechanical strength than the original SPI. Hydrogen permeability through SPI/PE CT membranes was 4.1–5.4 times lower than Nafion 212 and 1.4–1.9 times lower than the original SPI membrane. We have prepared a thin SPI/PE CT membrane (10 µm thickness), that showed comparable OCV (0.88 V), similar resistance compared to Nafion 212 and demonstrated more than 10 h of durability in a fuel cell test; suggesting that SPI/PE thin CT membrane can be applied for PEFC application.

The data presented in this article are related to polymer-polymer type charge-transfer blend membranes for fuel cell application. The visible spectra of the charge-transfer (CT) blend membranes indicated formation of CT complex in the blend membranes, and behavior of CT complex formation by polymers was clarified by Job plot of the visible spectra. The effect of fluorine for membrane property and fuel cell performance of CT blend membranes were evaluated by 19F NMR and overvoltage analysis, respectively.

Graphene oxide (GO) is potentially a useful electrolyte material for polymer electrolyte membrane fuel cells due to its high strength, excellent hydrogen gas barrier properties, hydrophilicity, and proton conducting acidic functional groups. Here, GO paper is prepared from aqueous dispersion by vacuum-filtration, and the hydrogen permeability (2 × 10 −2 barrer) is measured to be 3 orders of magnitude lower than Nafion (30 barrer) at 30 °C. The in-plane and through-plane conductivities are measured to be 49.9 and 0.3 mS cm −1 , respectively. This significant anisotropy is attributed to the lamellar structure of GO, and the physical anisotropy between the thickness and lateral size of the GO nanoplatelets. Interestingly, the in-plane conductivity of GO is comparable to the through-plane conductivity of Nafion. GO membrane fuel cells (GOMFCs) are fabricated. To compensate for the low in-plane conductivity of GO, whilst taking advantage of the excellent hydrogen gas barrier properties, extremely thin electrode-supported GOMFCs are prepared by spray painting GO directly onto the electrocatalyst layer. The effect of membrane thickness on cell performance is investigated. Decreasing membrane thickness by spray painting improves the power density from 3.7 mW cm −2 for a 50 μm-thick membrane-supported GOMFC, to 79 mW cm −2 for a 3 µm-thick, spray-painted membrane, electrode-supported GOMFC.

The efficiency and lifetime of mechanical devices is significantly decreased by friction and wear, significantly contributing to global energy consumption. We previously showed that multilayer polyethyleneimine/graphene oxide thin films, (PEI/GO)15, on steel display superlubricity against a steel counterface ball. Here, the coefficient of friction (COF) and wear of (PEI/GO)15 with six different counterface polymer balls is investigated in air and in nitrogen, with particular focus on the formation of tribological transfer films. The polymers polyoxymethylene (POM), polyetheretherketone (PEEK), polyethylene (PE), poly(methyl methacrylate) (PMMA), polycarbonate (PC), and polytetrafluoroethylene (PTFE) are utilized. The COF of (PEI/GO)15 vs steel is 0.35 in both air and nitrogen. In air, the COF ranges from 0.06 to 0.17 for all polymers. Significantly, in nitrogen, four polymers (POM, PEEK, PMMA and PC) display ultra-low friction (COF ∼0.02) whilst two do not (PTFE and PE). The wear tracks and transfer films are investigated using e.g. optical microscopy, electron microscopy, and Raman mapping, and the tribological behavior is correlated to the hydrophilicity and relative hardness of the polymer balls compared to GO.

Enhancing the fluxes in gas separation membranes is required for utilizing the membranes on a mass scale for CO2 capture. Membrane thinning is one of the most promising approaches to achieve high fluxes. In addition, sophisticated molecular transport across membranes can boost gas separation performance. In this review, we attempt to summarize the current state of CO2 separation membranes, especially from the viewpoint of thinning the selective layers and the membrane itself. The gas permeation behavior of membranes with ultimate thicknesses and their future directions are discussed.

The transport of small gases (H2, CO2, N2, O2) through a series of novel membranes based on necklace-shaped inorganic polymers (DMS@POSS), in which a polyhedral oligomeric silsesquioxane (POSS) cage unit and soft chains of oligo-dimethyl siloxane (DMS) were alternately connected, was investigated. The influence of the DMS chain length and crosslinking density of the DMS@POSS on membrane properties were studied. The membranes revealed characteristic structure-property relation towards both glass transition and gases transport. Specifically, clear dependence of properties from the length of DMS units (or overall siloxane content) was revealed. Gas transport properties, when compared to state-of-art polydimethylsiloxane and commercial silicone rubber, demonstrated significantly higher selectivity of DMS@POSS for carbon dioxide (in CO2/N2), hydrogen (in H2/N2) and oxygen (in O2/N2) but lowered permeability, proportional to the amount of POSS in the material. With a precise control over mechanical and thermal properties compared to conventional silicone rubbers, described materials could be considered as materials of choice in niche gas separation or other applications.

Polymer electrolyte membrane fuel cells are an efficient and clean alternative power source, but high cost impedes widespread commercialization. The fuel cell membrane, e.g., Nafion, contributes significantly to this cost, and therefore, novel alternatives are required. Temperature is also an important factor; high temperature operation leads to faster reaction kinetics, lower electrocatalyst loading, and improved water management, thereby further reducing cost. However, higher temperature puts greater demands on the membrane. Conductivity is related strongly to humidification, and therefore, this generally decreases above 100 °C. Nanocellulose membranes for fuel cells in which the proton conductivity increases up to 120 °C are reported here for the first time. The hydrogen barrier properties are far superior to conventional ionomer membranes. Fuel cells with nanocellulose membranes are successfully operated at 80 °C. Additionally, these membranes are environmentally friendly and biodegradable.

A novel class of alkaline anion exchange membrane (AAEM) is presented, in the form of KOH-modified multilayer graphene oxide paper (GOKOH). Such membranes can be easily fabricated at large scale with varying thickness using conventional filtration techniques, and have high tensile strength (24.5 MPa). However, a large degree of swelling is observed. SEM investigations show that the morphology of GO changes after KOH-treatment, whilst XPS measurements and XRD analysis confirm successful chemical modification. The hydrogen gas permeability is several orders of magnitude lower than conventional polymer-based ionomer membranes. The maximum anion conductivity is 6.1 mS/cm at 70 °C, and the dominant charge carrier is confirmed to be OH− by utilization of anion and proton-conducting blocking layers. The ion exchange capacity is 6.1 mmol/g, measured by titration. A water-mediated reverse Grotthuss-like mechanism is proposed as the main diffusion mode of OH− ions. Finally, a prototype AAEM fuel cell is fabricated using a GOKOH membrane, confirming the applicability to real systems.

Polymer electrolyte membrane fuel cells (PEMFCs) using hydrogen as fuel are efficient and clean energy generating devices. Commercialization of fuel cells is however slow, in particular due to high cost of the materials used to fabricate proton exchange membrane (PEM). Nafion®, a benchmark fluorinated polymer used as PEM, contributes significantly to the cost of fuel cell devices and therefore alternative materials are needed. The high proton conductivity of Nafion (i.e. ~100 mS/cm) has made this polymer the main material for PEMs, since its discovery in the late 1960s. However, it has number of disadvantages additionally to high cost, such as degradation under corrosive conditions and difficulty in recycling. Numerous research groups work on synthesis of proton conducting polymers that could compete with Nafion. Among the available techniques sulfonation of hydrocarbon polymers is recognized as an effective approach to create new PEMs [Peckham, T. J. et al. Adv. Mater. 2010, 22, 4667–4690]. Nanocellulose (NC) is an environmentally friendly, very low-cost material that can be produced by processing of conventional cellulose, which is plant-derived, renewable, and most abundant, material resource in the world. Research into nanocellulose for various applications is accelerating rapidly. Both cellulose nanofibers (CNF) and cellulose nanocrystals (CNC) are attractive due to their intrinsic properties, such as mechanical strength, high gas barrier, and a chemical structure suitable for various modifications. Being a biodegradable polymer, it has an additional advantage over fluorinated polymers (such as Nafion) The majority of works that considered the use of nanocellulose in PEMFCs have investigated composites with conventional ionomers such as Nafion, with varying results [Jiang, G. P. et al. J. Power Sources 2015, 273, 697–706]. However, the use of non-composited nanocellulose membranes for PEMFCs is a completely novel topic for research. Nanocellulose is an attractive polymer platform for PEMs, however its application for this purpose is not widely explored. The use of nanocellullose membranes in PEMFCs was pioneered by our group and previous works have demonstrated that both CNF and CNC membranes can work as a PEM in fuel cells. However, membranes made of pristine nanocellulose lacked sufficient proton conductivity, and required better stability in high temperature and humid environments. Namely, the inherent proton conductivity of nanocellulose is quite low: i.e. ~0.05 mS/cm for cellulose nanofiber (CNF) and ~4 mS/cm for cellulose nanocrystals (CNC) membrane [Bayer, T. et al., Chem. Mater. 2016, 28, 4805–4814] and thus requires significant improvement. Conventional approaches for nanocellulose modification (e.g. TEMPO-oxidation, backbone sulfonation) can achieve better proton conductivity only by sacrificing other properties (i.e. the mechanical, aqueous, and chemical stability) [Isogai A. et al. Nanoscale, 2011, 3, 71-85]. In contrast, crosslinking of nanocellulose was shown to provide improved mechanical properties and reduced swelling in water [Quellmalz et al. ACS Biomater. Sci. Eng. 2015, 1, 271−276], as well as better proton conductivity when an appropriate crosslinking agent is used (i.e. strong acid and good proton donor) [Seo J. A. et al. Ionics 2009 15, 555–560]. In this work we used chemical crosslinking of nanocellulose with sulfonic acid in order to achieve the required properties for PEM applications. Sulfosuccinic acid (SSA) was used as a crosslinking agent. Crosslinking of cellulose nanofibers (CNF) and cellulose nanocrystals (CNC) membranes was performed in a hot-press, to form SSA-x-CNF and SSA-x-CNC membranes. Initial tests resulted in membranes of < 10 µm thickness; significantly decreased swelling; stability in boiling water; and increased through-plane conductivity by 2 orders of magnitude. The findings so far confirm the hypothesis that a proper crosslinking agent can turn nanocellulose into an effective proton conductor as well as improving other relevant properties. Investigation into the effect on mechanical strength, chemical stability and fuel cell performance is still underway and will be also reported.

The effect of thickness in multilayer thin-film composite membranes on gas permeation has received little attention to date, and the gas permeances of the organic polymer membranes are believed to increase by membrane thinning. Moreover, the performance of defect-free layers with known gas permeability can be effectively described using the classical resistance in series models to predict both permeance and selectivity of the composite membrane. In this work, we have investigated the Pebax&reg, MH1657/PDMS double layer membrane as a selective/gutter layer combination that has the potential to achieve sufficient CO2/N2 selectivity and permeance for efficient CO2 and N2 separation. CO2 and N2 transport through membranes with different thicknesses of two layers has been investigated both experimentally and with the utilization of resistance in series models. Model prediction for permeance/selectivity corresponded perfectly with experimental data for the thicker membranes. Surprisingly, a significant decrease from model predictions was observed when the thickness of the polydimethylsiloxane (PDMS) (gutter layer) became relatively small (below 2 &micro, m thickness). Material properties changed at low thicknesses&mdash, surface treatments and influence of porous support are discussed as possible reasons for observed deviations.

Here we report a preferential CO2 separation membrane consisting of a nanometer-thick TiO2 layer incorporated with phtalic acid (PA) molecules on polydimethylsiloxane (PDMS) (PA@TiO2/PDMS). Incorporated PAs in TiO2 act as CO2-philic pores for preferential CO-2 permeation over nitrogen. CO2 binding to the PA incorporated in TiO2 is confirmed by the density functional theory calculation (DFT). As a result, membranes with of PA@TiO2 layer demonstrated much higher selectivity to CO2 for mixed CO2/N2 gas separation compared to a conventional PDMS membrane. The exceptional selectivity of the composite layer alone (>150) was estimated by a resistance model.

Multilayers of polyethyleneimine and graphene oxide, (PEI/GO)15, were coated onto steel substrates via electrostatic layer-by-layer (LbL) deposition, and their tribological properties were investigated as solid lubricants. The coefficient of friction (COF) and specific wear rate (SWR) were measured against a poly(methyl methacrylate) (PMMA) counterface ball, in various gas environments with different oxygen concentrations. The COF and SWR both significantly decreased with decreasing oxygen content. Detailed surface characterization of the contact area of the counterface ball revealed that continuous transfer films were formed in oxygen-free environments, but not in oxygen-rich environments. This is attributed to an increased proportion of sp3 bonding in the wear debris in the presence of oxygen (as confirmed by Raman spectroscopy), as well as possible suppression of wear debris adhesion on the counterface ball due to oxygen adsorption on the surface.

A novel class of core-shell- and hollow-structured MnCO3/TiO2 composites was synthesized by titania nanocoating on MnCO3 microspheres via two-step liquid-phase deposition at room temperature. Morphological change from core-shell to hollow microparticles was possible in the prepared samples by controlling prereaction time of MnCO3 and [NH4]2TiF6. Upon the prereaction process, the core of the core-shell MnCO3/TiO2 became highly porous, and a honeycomb-like surface that resembled the orientation of self-assembled MnCO3 nanocrystals was developed. The MnCO3 core was completely removed after 6 h prereaction. Calcination at 600 °C resulted in the transformation of both core-shell- and hollow-structured composites to Mn2O3/TiO2 anatase microspheres that retained their original morphologies. X-ray diffraction, field-emission scanning electron microscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, and electron probe microanalysis were employed for microsphere characterization. As the first trial for application of the synthesized materials, solid-extraction of organics from aqueous media was examined using methylene blue (MB). Both types of Mn2O3/TiO2 composites showed very fast adsorption of MB with high extraction values of 5.2 and 6.4 μmol g(-1) for the core-shell and hollow structures, respectively. Current work provides a new approach for facile fabrication of titania-metal oxide nanocomposites with unique morphological features and promising application possibilities.

We present hybrid films consisting of a composite prepared from polystyrene (PS) and titanium dioxide (titania; TiO2) and molecularly imprinted with 1-pyrenebutyric acid (PBA). The interaction of PBA with the polymer is shown to occur via binding of the carboxylic group to TiO2 and hydrophobic interaction of the pyrene moiety with the PS network. We investigated the effects of the PS fraction on morphology, imprinting properties, and guest binding. The template could be completely removed by incubating the films in an acetonitrile solution of pyrene, which is due to the stronger π–π interaction between PBA and pyrene than the interaction between PBA and its binding site. A guest binding study with pyrene, 1-aminopyrene, pyrenemethanol, and anthracene-9-carboxylic acid showed that the hybrid films possessed selectivity and much higher binding capacity for PBA. This study demonstrates the first case of clear PS-assisted imprinting, where the π–π interaction of the template with a linear (non-crosslinked) polymer creates selective binding sites and enhances the binding capacity. This is a driving force for guest binding in addition to the interaction of the template/analyte with TiO2. All molecularly imprinted films displayed better binding, repeatability and reversibility compared to the respective non-imprinted films.

Alternate TiO2 gel ultrathin films assembled with a macrocyclic carboxylic acids of tetrakis-4-carboxyphenyl porphine (TCPP) or tetra-4-carboxylphthalocyanine cobalt (II) (Co-TCPc) were prepared by the surface sol–gel process. To confirm the film growth and imprinting effect, quartz crystal microbalance (QCM) and UV–vis spectroscopy measurements were employed. The binding of TCPP was 1.2–14.3 times more selective compared to structurally related macrocyclic guest molecules. Among other findings, tetrakis-4-carboxymethyloxyphenyl porphine (TCMOPP) that has a spacer ( O CH2 ) between the phenyl rings and carboxylic acid moieties of TCPP showed a significantly lower binding efficiency equal to 0.07, regardless of its similar molecular structure to the template molecule. Structural difference of porphyrin and phthalocyanine analogs could be also selectively discriminated: the TCPP imprinted film showed ca. 13 times higher selectivity for recognition of TCPP itself from the mixture of TCPP and Co-TCPc. Characterization by AFM demonstrated that the TiO2/TCPP film has highly uniform surface and ultrathin thickness, while both TEM and SEM studies confirmed the immobilized structures of TCPP inside the film.

A fibre optic long period grating (LPG) with an nano-assembled mesoporous coating of alternate layers of poly(diallyldimethylammonium chloride) (PDDA) and SiO 2 nanospheres was used for the development of a highly sensitive fibre-optic chemical sensor. Sensor fabrication involves a 2-stage process: firstly, the deposition of the base mesoporous thin film (PDDA/SiO 2 ) over an LPG written in the optical fibre using a layer-by layer technique, followed by the infusion of a functional material into the porous film. The refractive index of the base mesoporous coating, determined at a wavelength of 633 nm using ellipsometry, was found to be 1.2. The infusion of the functional material into the coating resulted in a significant change in the RI of the coating, producing a dramatic change in the transmission spectrum of the LPG. The sensing mechanism exploited is based upon chemically induced desorption of the functional material from the mesoporous coating. The sensing of ammonia in aqueous solution was chosen as an example to demonstrate the sensing principle of the LPG sensor. The operation of the sensor was characterized using two functional materials, tetrakis-(4-sulfophenyl)porphine (TSPP) and polyacrylic acid (PAA). The device showed high sensitivity to ammonia with a response time less than 100 s and a limit of detection of 140 ppb when the TSPP infused (PDDA/SiO 2 ) film was employed as a sensitive element.

Nano-assembled thin films prepared by a layer-by-layer approach on QCM resonators were used as sensitive elements for monitoring relative humidity. Different types of films, polymer-based (PDDA/PSS)n film and porphyrin-based (PDDA/TSPP)n and (PDDA/MnTSPP)n films (where n = 5, 10, and 15), showed linear responses to relative humidity changes in the range of 4–94%. Increase of the number of bilayers deposited on the QCM electrode enhanced the sensitivity to relative humidity. The porphyrin-based films showed ca. 4.5 times higher sensitivity towards relative humidity than the polymer-based films, owing to presence of the higher number of free sulfonic acid groups. Incorporation of the metal ion into the porphyrin pyrrole ring was not significant in sensitivity. However, all films showed a good reversibility to the stepwise changes of relative humidity and the response and recovery times (t90) were very fast within 15 s.

GC–MS analysis based on purge and trap sampling followed by Curie point thermal desorption was examined for the quantitative determination of 2,4,6-trichloroanisole in aqueous solutions. The method developed showed linearity in single ion monitoring mode over a TCA concentration range of 0.12–120 ng L−1 (parts-per-trillion).

An evanescent-wave optical fibre sensor modified with tetrakis(4-sulfophenyl)porphine (TSPP) and poly(allylamine hydrochloride) (PAH) bilayers using an layer-by-layer (LbL) approach was tested to measure the gas emitted from human skin. Optical intensity changes at different wavelengths in the transmission spectrum of the porphyrin-based film were induced by the human skin gas and measured as sensor response. Influence of relative humidity, which can be a major interference to sensor response, was significantly different when compared to the influence of skin emanations. Responses of the current optical sensor system could be considered as composite sensor array, where different optical wavelengths act as channels that have selective response to specific volatile compounds. Data obtained from the sensor system was analyzed through principal component analysis (PCA). This approach enabled to distinguish skin odors of different people and their altered physiological conditions after alcohol consumption.

The facile one-pot fabrication of anatase TiO2-coated multiwalled carbon nanotubes (MWCNTs) via a liquid-phase deposition process is demonstrated. Optimization of the deposition parameters of precu...