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Paper-based microfluidic devices are popular for their ability to automate multistep assays for chemical or biological sensing at a low cost, but the design of paper microfluidic networks has largely relied on experimental trial and error. A few mathematical models of flow through paper microfluidic devices have been developed and have succeeded in explaining experimental flow behavior. However, the reverse engineering problem of designing complex paper networks guided by appropriate mathematical models is largely unsolved. In this article, we demonstrate that a two-dimensional paper network (2DPN) designed to sequentially deliver three fluids to a test zone on the device can be computationally designed and experimentally implemented without experimental trial and error. This was accomplished by three new developments in modeling flow through paper networks: (i) coupling of the Richards equation of flow through porous media to the species transport equation, (ii) modeling flow through assemblies of multiple paper materials (test membrane and wicking pad), and (iii) incorporating limited-volume fluid sources. We demonstrate the application of this model in the optimal design of a paper-based signal-enhanced immunoassay for a malaria protein, PfHRP2. This work lays the foundation for the development of a computational design toolbox to aid in the design of paper microfluidic networks. ©

In this report, we documented novel strategy for the synthesis of bioactive polysubstituted 2-amino-4H-chromine derivatives under a heterogeneous Al-MCM-41-LDH@APTES (ALAM) catalysis. A synthetic procedure is developed to prepare Al-MCM-41-LDH@APTES (ALAM) heterogeneous basic catalysts. Mesoporous Al-MCM-41 is functionalized by known grafting chemistry via layered double hydroxide (LDH) nanosheets and (3-aminopropyl)triethoxysilane (APTES) moiety as a basic organocatalyst. The resulting catalysts contain amino group functionality on the external surface as well as inside the layers and the basicity can be tuned by the loading of APTES. The samples were fully characterized by 29Si and 13C CP/MAS NMR, infrared absorption spectroscopy, TEM, XPS, EDX, TGA, XRD, CO2-TPD, N2 adsorption isotherms measurements, and they were successfully examined for the cascade type Knoevenagel–Michael addition reactions. The product yields associated with these substrates were optimized, and key reaction parameters affecting the yields were identified. The present catalytic method is simple and robust for diversity oriented synthesis which proceeds good to excellent yields without generating any hazards waste. The broad substrate scope, excellent functional group compatibility makes this protocol highly useful towards synthesis of polysubstituted α-cyanoacrylates, α-cyanoacrylonitriles and 2-amino-4H-chromenes with an electron-donating or electron-withdrawing group. We have also successfully established a flow reaction system, gram-scale synthesis as well as catalyst recyclability up to six catalytic cycles without appreciable loss of its activity.

The abolition of environmental pollutants and production of hydrogen (H2) from water using a heterogeneous photocatalyst is a demanding science of the current scenario to solve the increasing environmental pollution and worldwide energy catastrophe in modern life. To validate this purpose, the design of low-cost and durable semiconductor-based photocatalysts with great light absorption capacity becomes the most challenging issue for researchers. Regarding this, herein the phosphotungstic acid (HPW)-anchored Zr6O4(OH)4(BDC)6 (UiO-66) metal-organic framework (MOF), i.e., HPW@UiO-66, has been prepared by a hydrothermal method and is efficient, stable, and capable of harvesting solar energy toward the degradation of tetracycline hydrochloride (TCH) and H2 production in the presence of a sacrificial donor. The ionic interaction between HPW and UiO-66 plays a key role toward the photostability and charge-transfer mechanism of the composite and is well characterized with X-ray diffraction, UV diffuse-reflectance spectroscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy. A total of 30 wt % HPW@UiO-66 shows a maximum degradation of about 87.24% of a 20 ppm TCH solution in 60 min of solar-light irradiation and about 353.89 μmol/h of H2 production. The conduction- and valence-band potentials are well characterized with Mott-Schottky measurement and a delay charge recombination process through electrochemical impedance spectroscopy. The proposed mediator-free Z-scheme-oriented electron-hole migration route is well supported by photoluminescence, and the scavenger test well explains the better charge-carrier separation and high catalytic performance of the prepared composite. This research will bestow an advantageous blueprint to fabricate novel and challenging photocatalysts toward the photocatalytic treatment of environmental pollutants and H2 evolution.

Achieving photocatalytic organic transformation reactions by using a visible light induced semiconductor-based photocatalyst is promising as a green and sustainable approach. In the present study, Au/Pd bimetallic alloy loaded amine (APTES) functionalised LDH (Layered double hydroxide)–MCM-41 composite was prepared through an in situ co-precipitation followed by a co-reduction method. The structural phases, textural properties, optical behaviour, morphological aspects, chemical states and functional groups of the photocatalysts were thoroughly analysed by powder X-ray diffraction (PXRD), high-resolution transmission electron microscopy (HRTEM), ultraviolet-visible diffuse reflectance (UV-vis DRS), fourier-transform infrared (FTIR) and X-ray photoelectron (XPS) spectroscopies. Moreover, the formation of an alloying structure between Au and Pd was confirmed from PXRD, HRTEM and UV-vis absorption spectra. We investigated one-pot synthesis of imines through photoalkylation of benzyl alcohol with nitrobenzene over Au/Pd bimetal alloy loaded on amine functionalised LDH–MCM-41 composite and it demonstrated imine yield of around 3.1 times (68%) more than the parent LDH (22%). The alloy nanoparticless efficiently harvest light and possess higher photocatalytic activity with respect to single Pd and Au nanoparticles. Due to the alloying structure develops charge heterogeneity on the surface of alloyed nanoparticles and enhances the interaction between metal surface with substrate molecule which promotes the coupling between photo generated benzaldehyde with aniline to form imine. Characterisation such as photoluminescence (PL), time-resolved photoluminescence (TRPL), electrical impedance spectroscopy (EIS) and photocurrent density measurements further proved the superior photoactivity towards imine synthesis. These photocatalytic tandem reactions, therefore, have great potential as an effective pathway for the one-pot organic synthesis and transformation of organics in an environmentally friendly way.

In a typical heterogeneous microfluidic immunosensor, the carrier fluid transports the target analytes to the antibodies immobilized on the channel surfaces with a thin liquid layer where they are captured. While single-phase systems (the carrier fluid being a liquid) are well studied, two-phase systems (the carrier fluid being a gas) are less explored. There in particular, the effect of transport parameters on the capture efficiency (a critical performance parameter) has not received much attention, and thus is the subject of study here. Hence, we have investigated the transport and capture of analytes in a two-phase heterogeneous microfluidic immunosensor wherein the target analytes in the gaseous phase are transported to the immobilized antibodies via gas–liquid interfacial mass transfer which strongly depends on flow variables of the gas phase flow. Parametric studies on capture efficiency using the properties of trinitrotoluene (TNT) were used to obtain the effects of important transport parameters on the capture of analyte molecules. The highlight of this work is the development of an empirical correlation between the capture efficiency and the gas-side non-dimensional interfacial mass transfer coefficient (Sherwood number, Shg). This could help design of a two-phase microfluidic device with improved performance parameters to capture gaseous analytes.

Visible light harvesting by heterogeneous photocatalysts and their applications in organic transformation reactions for the synthesis of target molecules are quite demanding science in the current scenario. In this regard, herein, a novel metal (Au/Pd)-functionalized metal organic framework (UiO-66-NH2) was synthesized to carry out the Suzuki–Miyaura coupling (SMC) reaction under visible light irradiation at ambient conditions. In order to justify the claim regarding the formation of alloys, crystallinity, morphology, particle size, proper separation of excitons, elemental content and their environment, various sensitive characterization techniques such as XRD, XPS, HRTEM, BET surface area and UV-vis analysis were employed. A mechanistic approach by means of experimental investigations revealed that the strong LSPR effect of Au facilitated the transfer of electrons to the Pd surface to make the surface negatively charged and suitable for the activation of aryl halides. The formed electropositive Au nanoparticles were converted to Au0 by accepting the photo-induced electrons from pristine UiO-66-NH2 and made available only holes at VB for the activation of phenylboronic acid. Among all the synthesized photocatalysts (1 : 2), Au/Pd@UiO-66-NH2 showed the highest activity (>99%) with TOF = 426 h−1 in an EtOH/H2O medium towards the SMC reaction, and the highest activity of this catalyst was supported by the electron gas model, LSPR effect (UV-vis) and active species separation (PL) analysis. The bimetallic noble nanoparticle-anchored UiO-66-NH2 not only expands the synthesis scope of C–C coupling by the SMC reaction under ambient conditions but will also inspire the further exploration of the activation of various reactants towards a wide range of organic transformation reactions.

A series of sulphate modified Al-MCM-41 acid catalysts are synthesized following impregnation and co-condensation methods The physico-chemical characterizations of all the samples are done by XRD, FT-IR, TGA/DTA, TPD, N 2 adsorption and desorption study, SEM, HRTEM and EDAX etc. The structural advantages of Al-MCM-41 such as large specific surface area, wide pore size and pore volume and Bronsted and Lewis acid sites favor the coupling reaction. The catalysts endorsed the direct addition of alcohols to alkynes as well as their coupling with styrenes. The various combinations of alcohols with alkynes and styrenes are compatible with diverse functional groups to synthesize a substituted aryl ketones, as well as olefins with good to excellent yields. Additionally, the approach is advantageous in terms using alcohols, discounting the pre-functionalization and generation of waste by-products. Used precursors, alkynes and styrenes, are valuable since they are stable and found in many biologically active compounds. This current research work provides supplements to C C bond formation methodologies as a single step with atom economy and recyclable approach under mild and environmentally benign conditions.

Since Andreas Manz first introduced the microchip technology for chemical applications back in the 1990s, the field of `microfluidics' has expanded widely and microfluidic tools have become ubiquitous in life sciences research. However, pumps and controllers associated with most current microfluidic chips continue to be bulky and costly. A new class of microfluidic devices in which flow channels are composed of multidimensional (2D or 3D) shapes of porous materials is becoming increasingly popular. The ability of porous materials to wick fluids obviates the need for pumps, making such devices portable, low-cost, and ideal for use in low-resource settings. Such devices are broadly referred to as ``paper microfluidic devices''. The ability to manipulate fluids in paper microfluidics has progressively increased over the past decade and such devices are currently being used to develop highly sensitive and multiplexed low-cost diagnostic/sensing devices. In this article, we review the area of paper microfluidics covering the basic fluid physics, methods of fabrication, flow control tools, applications in diagnostics/sensing, and applications in other emerging areas like tissue engineering and power storage. This review is targeted to a broad audience that does not have prior exposure to the field of paper-based microfluidics. Through this article, we wish to invite researchers from multiple backgrounds to contribute to further development in this new and exciting area of research.

Photocatalytic organic transformations driven by functionalised metal organic frameworks (MOFs) are a green perspective for fine chemical synthesis. In the class of highly porous materials, MOFs are unparalleled in their degree of tunability and structural diversity and range of physical and chemical properties such as large surface area, permanent porosity, large void volumes, and framework flexibility, because of which they can act as a sustainable alternative for inorganic semiconductors. MOFs are the latest class of ordered porous solids being intensively studied as a novel class of hybrid organic–inorganic materials as nanophotocatalysts in the field of chemistry, materials science, chemical engineering, etc. Although the photocatalytic application of MOFs is still in the early stages compared with their other applications such as gas storage, separation, and heterogeneous catalysis, the currently available results have revealed that functionalised MOFs are very active as photocatalysts. The present review aims to discuss the various synthetic methods, post-synthetic modifications, MOF catalysed organic reactions and proposed mechanistic pathways for photoinduced organic transformations.

For enhancing solar energy conversion and environmental remediation, noble metal plasmonic photocatalysis originating from the effectual light absorbance and confinement of surface plasmons provides a new promising route. In the present study, by integrating these two aspects, a series of ternary Ag@Ag3VO4/ZnCr LDH heterostructures have been prepared by an in situ hydrothermal followed by co-precipitation method. In this method, there is self-assembling of Ag3VO4 nanoparticles on the brucite surface of the LDH material along with partial reduction of Ag+ to Ag. The phase identity, optical response, and morphological structure of the heterostructure photocatalysts were systematically characterized through PXRD, HRTEM, UV-Vis DRS, PL, and XPS methods. The resulting monodisperse Ag nanoparticles deposited on LDH materials offer a heterogeneous interaction at the interface and exhibit high photocatalytic activity towards generation of O2 and oxidation of phenol. Evaluation of photocatalytic activity showed that 40 wt% of Ag3VO4 modified LDH is the most effective photocatalyst for O2 evolution (571 μmol) and phenol oxidation (93%). The highly improved photocatalytic performance of the composite was ascribed mainly to the SPR effect of Ag nanoparticles, Schottky barriers formed at the interface of LDH and Ag3VO4 nanoparticles, and strong coupling between Ag, Ag3VO4 and LDH. The electrochemical studies such as LSV, CV, EIS and Tafel plots further support the high rate of photoactivity towards O2 evolution and phenol oxidation. These newly designed plasmonic Ag–LDH nanoheterostructures may offer a promising strategy for maximum light absorption and be authoritative in meeting environmental claims in the future.

Potent utilisation of a huge amount of red mud generated from aluminium industries is a threat to the environment. In the present work the red mud is successfully utilised as an effective photo catalyst for removal of Cr (VI) and malachite green from waste water. A series of red mud/MCM-41composite (RMCM) is developed by simple sol-gel method. The materials are characterised by N 2 ads-des studies, XRD, FTIR, UV–vis DRS, PL and electrochemical studies. From the XRD study it is confirmed that red mud contains both hematite (α-Fe 2 O 3 ) and goethite (α-FeOOH) phases of iron. Their synergetic effect develops a p - n junction and expedites the photo catalytic activity of the material. The structural advantages of MCM-41 plays a vital role for suppressing the e − /h + recombination which is confirmed from the PL study. The RMCM (1:1) exhibits the maximum reduction (85%) of 20 mg L −1 of Cr (VI) solution and oxidation of malachite green (97%). The oxidation and reduction processes provide beneficial method for purification of the waste water and environmental restoration. Further the applications of the RMCM can be extended for absorption of heavy metals, generation of H 2 energy by splitting water and photo catalytic organic transformation reactions. The current work will be beneficial for the researchers working in this field.

Porous graphitic carbon nitride (g-C3N4) was synthesized by taking melamine and ammonium bicarbonate through single-step calcination method followed by ultrasonication to obtain exfoliated porous g-C3N4 (2D) nanosheets. Further enhancement of photocatalytic performance, g-C3N4 nanosheet (2D) was further modified with different weight percentage of (1, 3, 5, and 7) of MnO2. The introduction of α-MnO2 onto the g-C3N4 nanosheet establishes an interlayer channels to promote the migration of charge carriers through the valence band and conduction band of the prepared composite MnO2@g-C3N4. The transformation of photo induced charge carriers adopt the Z-scheme mechanism rather band-transfer mechanism. The accumulated photo generated electrons in conduction band of g-C3N4 is more electro negative than the potential of (O2/O2–.) and able to reduce oxygen to superoxide (O2–.) radical. At the same time, the holes in valence band of α-MnO2 are more electro positive than the potential of (OH–/OH.) and help in oxidate OH– to hydroxyl (OH.) radical. Among all the composites, 3 wt% MnO2 modified g-C3N4 shows the best photocatalytic oxidation efficiency towards all the aromatic alcohols. In presence of visible light, heterojuction formation, and formation of active charged species (OH. and O2–.) were mostly responsible for photocatalytic oxidation of aromatic alcohols through free radical mechanism.

A series of ternary Cu@CuO–g-C3N4/MCM-41 photocatalysts have been synthesized by varying the percentage of Cu using simple impregnation and co-condensation methods. The physico-chemical characterization of all the samples was determined using XRD, FTIR, UV-Vis DRS, PL, N2 ads–des studies, SEM and XPS HRTEM, EDAX, EIS and MS. The structural advantages of MCM-41, allow the uniform distribution of g-C3N4 and coexistence of Cu2+ along with Cu0 without using a reducing agent. The presence of g-C3N4 helps to shift the Fermi level of CuO towards more negative values due to accumulation of photogenerated electrons on the surface. It favours charge separation by creating a Schottky barrier at the junction. The 4 wt% Cu loaded over g-C3N4/MCM-41 exhibits a maximum 750 μmol 2 h−1 of H2 evolution under visible light irradiation with an apparent energy conversion efficiency of 24.8%. The enhancement in catalytic activity has been explained on the basis of synergism between g-C3N4 and Cu2+ and the SPR effect of Cu which also acts as a co-catalyst present on the surface of photocatalysts.

This work reports an amine modified meso Al2O3@MCM-41, particularly the ordered mesoporous silica, as a catalyst for the formylation of amines with carbon dioxide (CO2) and with dimethylamine-borane (DMAB) as a green reducing source. This newly developed catalytic system represents a heterogeneous and environmentally benign protocol. Besides this, the catalyst could be reused for five consecutive cycles without any significant loss in its catalytic activity towards the synthesis of formamides. The amine modified meso Al2O3@MCM-41 catalysts were well characterized by high and low angle XRD, temperature programmed desorption (TPD), BET-surface area, TGA/DTA and FT-IR analysis techniques. The effect of various reaction parameters such as temperature, CO2 pressure, time and the ratio of substrates to DMAB for the synthesis of formamides has been investigated. The developed protocol can be applicable for the synthesis of most important key intermediates like formoterol, orlistat, leucovarin and iguratimod in biologically active compounds.

Paper-based microfluidic devices are rapidly becoming popular as a platform for developing point-of-care medical diagnostic tests. However, the design of these devices largely relies on trial and error, owing to a lack of proper understanding of fluid flow through porous membranes. Any porous material having pores of multiple sizes contains partially saturated regions, i.e., regions where less than 100% of the pores are filled with fluid. The capillary pressure and permeability of the material change as a function of the extent of saturation. Although methods to measure these relationships have been developed in other fields of study, these methods have not yet been adapted for paper for use by the larger community of analytical chemists. In the current work, we present a set of experimental methods that can be used to measure the relationships between capillary pressure, permeability, and saturation for any commercially available paper membrane. These experiments can be performed using commonly available lab instruments. We further demonstrate the use of the Richards equation in modeling imbibition into two-dimensional paper networks, thus adding new capability to the field. Predictions of spatiotemporal saturation from the model were in strong agreement with experimental measurements. To make these methods readily accessible to a wide community of chemists, biologists, and clinicians, we present the first report of a simple protocol to measure the flow rates considering the effect of partial saturation. Use of this protocol could drastically reduce the trial and error involved in designing paper-based microfluidic devices.

Detection of minute quantities of target antigens in serum samples (consisting of a mixture of proteins/biomolecules) can be achieved by enhancement of the capture efficiencies of heterogeneous immunosensors. An important process parameter which affects the capture of target analytes in such immunosensors is the pH of the solution as the target proteins present in the serum samples are charged molecules. Here, we investigated the capture of prostate-specific antigens (PSAs), first in a mixed-analyte system wherein the solution contained two other non-specific proteins along with the target analyte, using the surface plasmon resonance spectroscopy. There are no reports on the detection of antigens in a mixed system based on the optimization of the pH values of the carrier fluid, and this is the motivation of the present work. Further, we studied interference effects caused by the presence of these non-specific proteins in the mixed-analyte systems by artificially increasing the ratio of the interfering proteins to that of the target protein. Eventually PSA spiked into the rabbit serum samples was captured through the optimization of the pH of the solution. We could detect PSA in the serum samples when diluted to 100 times or more, where the amounts of other interfering proteins were ~ 66 times that of the amount of PSA. This study proposes a heterogeneous immunosensor to detect the target analytes in the diluted serum samples by tuning pH the of solution mixture, which can be utilized to detect disease biomarkers in serum samples.

The current research paper deals with the study of palladium doped TiO2 based photocatalytic system to remove cyanide from coke oven wastewater. The photocatalytic activity was improved by employing hydroxyapatite nanoparticles, which serves to enhance the concentration of cyanide near the photoactive sites of TiO2 and also prevents its agglomeration. Further, to enhance the rate of photocatalytic degradation of cyanide under visible light irradiation an iron tetracarboxy phenyl porphyrin sensitizer (Fe-TCPP) was employed. The structural and morphological characterization of the synthesized catalysts were carried out by Fourier transformation infrared spectroscopy (FTIR), X-ray diffraction (XRD), photoluminescence (PL) emission spectra, field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS) and ultraviolet diffuse reflectance spectroscopy (UV- DRS). The photocatalytic activity of the TiO2-Pd-HAP-Fe-TCPP- nanocomposite has been evaluated on degradation of cyanide under visible light irradiation using a photocatalytic reactor system. The results demonstrate the existence of synergistic effect between TiO2-Pd-HAP and Fe-TCPP sensitizer on removal of cyanide. Almost 90% of cyanide degradation was achieved at pH 11 within a short time span of 90 min, using the TiO2-Pd-HAP -Fe-TCPP nanocomposite. The photocatalytic degradation of cyanide by the nanocomposite follows pseudo-first order kinetics. The apparent rate constant (kapp) value of the TiO2-Pd-HAP-Fe-TCPP nanocomposite is estimated to be 11.6 and 4.3 time higher than that of bare TiO2 and TiO2-Pd-HAP respectively. Further, at this condition, >90% toxicity removal was achieved in the photocatalytic system even at a very high initial concentration of cyanide. Therefore, the Fe-TCPP-TiO2-Pd-HAP nanocomposite system can be considered as an alternative technique for removal of cyanide from coke oven wastewater.

Higher capture efficiency of biomarkers in heterogeneous immunosensors would enable early detection of diseases. Several strategies are used to improve the capture efficiency of these immunosensors including the geometry of the system along with the transport and reaction parameters. Having a prior knowledge of the behavior of the above parameters would facilitate the design of an efficient immunosensor. While the contributions of the transport and reaction parameters toward understanding of the mechanism involved in capture have been well studied in the literature, their effect in combination with the geometry of the sensors has not been explored until now. In this work, we have experimentally demonstrated that the capture efficiency of the antigen-antibody systems is inversely related to the size of the sensor patch. The experimental system was simulated in order to get an in-depth understanding of the mechanism behind the experimental observation. Further, the extent of heterogeneity in the system was analyzed using the Sips isotherm to obtain the heterogeneity index (α) and the reaction rate constant (K(D)) as fitted parameters for a sensor patch of 1.5 mm radius. The experimental kinetic data obtained for the same sensor patch matched reasonably with the simulation results by considering K(D) as the global affinity constant, which indicated that our system can be considered to be homogeneous. Our simulation results associated with the size dependency of the capture efficiency were in agreement with the trends obtained in our experimental observations where an inverse relation was observed owing to the fact that the mass-transfer limitation decreases with the decrease in the size of the sensor patch. The possible underlying mechanism associated with size dependency of capture efficiency was discussed based on the time-dependent radial variation of captured antigens obtained from our simulation results. A study on the parametric variation was further conducted for the nonmixed and mixed systems on the transport (Deff), reaction (K(D)), and geometric parameters (R). Two different correlations were established for the nonmixed and mixed systems between the capture efficiency (f) and a nondimensional number (t(D)/t(R)) consisting of the above-mentioned parameters. Such unified relations will be useful in designing heterogeneous immunosensors and can be extended to microfluidic immunosensors.