Interface-induced terahertz persistent photoconductance in rGO-gelatin flexible films

Luminescent lanthanide-containing gelatin/polydextran/laponite nanocomposite double-network hydrogels for processing and sensing applications

Lanthanide-containing nanomaterials have gained significant popularity for their utilization in polymeric networks, enabling the creation of luminescent nanocomposites for advanced applications. In this study, we developed a new type of lanthanide-containing nanocomposite hydrogels by incorporating terbium-containing laponite (Tb3+@Lap) into the networks of polyethyleneimine-modified gelatin/polydextran aldehyde (PG/PDA) through dynamic bonds. The structures and properties of the Tb3+@Lap-containing nanocomposite double-network (ncDN) hydrogels were comprehensively investigated in comparison with the DN hydrogels with a pure polymeric network and the Lap-containing ncDN hydrogels. The PG/PDA/Tb3+@Lap ncDN hydrogels with multiple dynamic bonds (i.e., imine bonds, coordination bonds, hydrogen bonds, and electrostatic interactions) exhibited remarkable characteristics of shear-thinning and self-healing, making them suitable for the construction of hydrogel scaffolds on a macroscale using fabrication techniques such as electrospinning and 3D printing. Moreover, the PG/PDA/Tb3+@Lap ncDN hydrogels have been demonstrated to act as sensitive and selective luminescent sensors for detecting copper ions. Taken together, a versatile lanthanide-containing ncDN hydrogel platform capable of dynamic features is developed for processing and sensing applications.

Preparation of chitosan/gelatin-based functional films integrated with carbon dots from banana peel for active packaging application

Carbon dots (CDs) were manufactured with banana peels using a hydrothermal method (200 °C for 6 h). The synthesized CDs were spherical particles with a size of 1-3 nm having carboxyl groups and amine groups on the surface. CDs have been impregnated into chitosan/gelatin films to synthesize multifunctional packaging films. The composite film showed a slight decrease in transparency but a significant increase in UV protection properties. The fabricated film displayed strong antioxidant efficacy showing >74 % DPPH and 99 % ABTS radical scavenging potential. The film also unveiled substantial antibacterial activity against the foodborne pathogenic bacteria, Listeria monocytogenes, fully eliminating the growth of these bacteria within 6 h of exposure. The chitosan/gelatin film containing CD was used for minced meat packaging, and the film delayed bacterial growth (< 1 Log CFU/g after 24 h) and maintained the meat color even after 24 h of storage at 20 °C. The CD-added chitosan/gelatin functional film has a high probability of application in active food packaging, especially for extending the shelf life of packaged meat and maintaining its aesthetic quality.

Chitosan/Starch-Based Active Packaging Film with N, P-Doped Carbon Dots for Meat Packaging

Nitrogen, phosphorus-doped green-tea-derived carbon dots (NP-CDs) incorporated chitosan/starch (Chi/St) based multifunctional nanocomposite films were prepared. FE-SEM images verified a homogeneous distribution of CDs with minimum aggregation in the fabricated films. Incorporating NP-CDs led to enhanced UV-light blocking (93.1% of UV-A and ∼99.7% of UV-B) without significantly affecting the films' water transparency and water vapor permeability. Besides, incorporating NP-CDs into the Chi/St films enhanced antioxidant activity (98.0% for ABTS and 71.4% for DPPH) and displayed strong antibacterial activity against L. monocytogenes, E. coli, and S. aureus. Wrapping the meat in the prepared film and storing it at 20 °C has been shown to reduce bacterial growth (less than 2.5 Log CFU/g after 48 h) without significantly altering the actual color of the wrapped meat. The Chi/St film loaded with NP-CD has high potential as an active packaging material to ensure safety and extend the shelf life of meat products.

Pore-structure regulation of biomass-derived carbon materials for an enhanced supercapacitor performance

Herein, we report a dual-porogen synthesis strategy to fabricate a micro-/meso-/macroporous carbon material for supercapacitors from biomass. The hierarchically porous carbon material was produced in a facile way by pyrolyzing C₁₀H₁₄N₂Na₂O₈/KOH (dual-porogen) and walnut peel (biomass carbon source) along with HCl solution etching. Such an admirable dual-porogen strategy opened up the closed pores and broadened the range of pore distribution for the carbon material from 0.55-1.76 nm to 0.59-2.53 nm as the mass ratio of walnut peel and C₁₀H₁₄N₂Na₂O₈ increased from 1 : 0 to 1 : 2, making up for the shortcomings of the narrow microporous distribution caused by the use of potassium hydroxide exclusively. As expected, the hierarchically porous carbon materials with a regulated structure with an appropriate pore volume, broadened pore-size distribution, ultrahigh specific surface area, as well as the effective hetratom dopping manifested its remarkable capacitor performances. The highest specific capacitance for a porous carbon material achieved was 557.9 F g^-1 (at 1 A g^-1) and 291.0 F g^-1 (at 30 A g^-1). The highest power density could reach up to 5679.62 W kg^-1, and energy density achieved was 12.44 W h kg^-1, thus greatly promoting its use in the design and synthesis of high-performance electrode materials for supercapacitors.

Electrical stimulation of neonatal rat cardiomyocytes using conductive polydopamine-reduced graphene oxide-hybrid hydrogels for constructing cardiac microtissues

The development of diversified biomaterials in tissue engineering has been promoted by growing research into carbon-based nanomaterials. Usually, ideal scaffold materials should possess properties similar to the extracellular matrix of natural myocardial tissue. In this study, dopamine-reduced graphene oxide (GO), was prepared and doped into gelatin methacrylate (GelMA) hydrogels, resulting in novel conductive and mechanical properties for controlling cell growth. Cardiomyocytes (CMs) cultured on PDA-rGO-incorporated hydrogels (GelMA-PDA-rGO) had greater cytocompatibility than those cultured on GelMA hydrogels, as evidenced by higher cell survival rates and up-regulation of cardiac-relevant proteins. Finally, electrical stimulation was applied to facilitate the maturation of CMs which was seeded on different hydrogels. The findings revealed that electrical stimulation of conductive hybrid hydrogel scaffolds improved the orientational order parameter of sarcomeres (OOP). In addition, propagation of intercellular pacing signals, which improves the expression of gap junction proteins was noticed, likewise calcium handling capacity was present in conductive hybrid hydrogels compared to those in pure GelMA group. This study has shown that the combination of GelMA-PDA-rGO based conductive hydrogels and electrical stimulation possessed synergistic effects for engineering a more functional and mature myocardium layer as well as further application in drug screening and disease modeling in vitro.

Design of new bioinspired GO-COOH decorated alginate/gelatin hybrid scaffolds with nanofibrous architecture: structural, mechanical and biological investigations

The current research study deals with the design and investigation of novel bioinspired and biocompatible GO-COOH decorated hybrid polymeric scaffolds with nanofibrous architecture as biomaterials with highly appropriate features for functional restoration of damaged tissue. Gelatin and alginate, two biobased-polymers with excellent biocompatibility, high microenvironment biomimicry and ability for proper guidance of cell development in combination with carboxylated graphene oxide (GO-COOH), embody the matrix of electrospun hybrid scaffolds. The underlying principle is based on various types of interactions that can take place between the functionalities of the system's entities (proved by DLS) and their synergy in improving the structural integrity, mechanical tailorability and biological performances of the new nanofibrous GO-COOH decorated hybrid scaffolds. The nanofibrous structure along with the presence of GO-COOH are established by SEM. The new covalent bonds formed between various functionalities of the protein-polysaccharide-GO-COOH system are proved by FTIR and XPS. The physico-chemical state of GO-COOH lattices within the hybrid structures is investigated by Raman spectrometry. The interpenetrated network of bicomponent structures determines a 10-fold increase of Young's modulus as compared to monocomponent counterparts while the dispersion of GO-COOH significantly increases the elasticity of materials. The biological results (MTT and LDH assays) indicate a good cytocompatibility of crosslinked bicomponent AGS scaffolds; the metabolic cellular activity is substantially improved following the GO-COOH addition, suggesting that GO-COOH can support the cell adhesion, growth and proliferation.

Terahertz surface and interface emission spectroscopy for advanced materials

Surfaces and interfaces are of particular importance for optoelectronic and photonic materials as they are involved in many physical and chemical processes such as carrier dynamics, charge transfer, chemical bonding, transformation reactions and so on. Terahertz (THz) emission spectroscopy provides a sensitive and nondestructive method for surface or interface analysis of advanced materials ranging from graphene to transition metal dichalcogenides, topological insulators, hybrid perovskites, and mixed-dimensional heterostructures based on 2D materials. In this review paper, we start with the THz radiation mechanisms under ultrafast laser excitation. Then we concentrate on the recent progresses of THz emission spectroscopy on the surface and interface properties of advanced materials, including transient surface photocurrents, surface nonlinear polarization, surface states, interface potential, and gas molecule adsorption/desorption processes. This novel spectroscopic method can not only promote the development of new and compact THz sources, but also provide a nondestructive optical method for surface and interface characterization of photocurrent and nonlinear polarization dynamics of materials.

Confining Redox Electrolytes in Functionalized Porous Carbon with Improved Energy Density for Supercapacitors

It is a big challenge to improve the energy density of the carbon-based supercapacitors for wide applications. In this work, considering the properties of redox electrolytes, functionalized porous carbon has been synthesized with interconnected pores and oxygen functional groups, which is employed to well hold the redox electrolyte ions. As a result, the functionalized porous carbon shows a high capacitance of 454 F g^-1 at a current density of 1 A g^-1 and can maintain 88% of the initial capacitance after 10 000 charge-discharge cycles at 10 A g^-1. Especially, the as-prepared asymmetric supercapacitor obtains high energy density of 36.9 W h kg^-1 at the power density of 225 W kg^-1. This new design strategy by coordinating carbon materials with the redox electrolytes will guide the development of high-energy density supercapacitors.

Interface Properties Probed by Active THz Surface Emission in Graphene/SiO2/Si Heterostructures

Graphene/semiconductor heterostructures demonstrate an improvement of traditional electronic and optoelectronic devices because of their outstanding charge transport properties inside and at the interfaces. However, very limited information has been accessed from the interfacial properties by traditional measurement. Herein, we present an active THz surface emission spectroscopy for the interface build-in potential and charge detrapping time constant evaluation from the interface of graphene on SiO₂/Si (Gr/SiO₂/Si). The active THz generation presents an intuitive insight into the depletion case, weak inversion case, and strong inversion case at the interface in the heterostructure. By analyzing the interface electric-field-induced optical rectification (EFIOR) in a strong inversion case, the intrinsic build-in potential is identified as -0.15 V at Gr/SiO₂/Si interface. The interface depletion layer presents 44% positive THz intrinsic modulation by the reverse gate voltage and 70% negative THz intrinsic modulation by the forward gate voltage. Moreover, a time-dependent THz generation measurement has been used to deduce the charge detrapping decay time constant. The investigation will not only highlight the THz surface emission spectroscopy for the graphene-based interface analysis but also demonstrate the potential for the efficient THz intrinsic modulation as well as the enhancement of THz emission by the heterostructures.

Enhanced polarization-sensitive terahertz emission from vertically grown graphene by a dynamical photon drag effect

Improving terahertz (THz) emission from graphene is a challenge for graphene-based THz photonics as graphene demonstrates a weak light-matter interaction. With a unique ultra-black surface structure, vertically grown graphene (VGG) is proposed to enhance the light-matter interaction and further enhance THz emission. Herein, enhanced THz radiation is observed by THz time-domain emission spectroscopy from VGG compared with single-layer graphene. The radiated THz amplitude shows a linear dependence on pump power, which demonstrates a second order nonlinear effect. Considering the symmetry of VGG on a substrate, we can exclude the optical rectification effect and photogalvanic effect (PGE) by the D_6h point group with centrosymmetry. Thus we analyze the transient photocurrent related to THz emission only by the photon drag effect (PDE). The polarization-sensitive THz radiation signals are wave-vector reliant and demonstrate cos 2φ and sin 2φ dependence on the polarization angles of the pump laser. This is consistent with the theoretical analysis of PDE. Our results show the enhanced, ultrafast, broadband THz radiation property of VGG, which paves the way for high performance THz emitters and THz detectors based on graphene materials.