PBAT is a biodegradable polymer which has been recently used to make electromagnetic shielding materials in combination with CNTs. Because of its mechanical strength, PBAT has also been combined with PLA by melt-blending to make PBAT/PLA/CNT composites. Ciprofloxacin is a commonly used antibiotic which is difficult to remove via conventional wastewater treatment methods, and has been detected at significant levels in the environment. It is toxic to certain aquatic organisms, 143 and can interact with bacteria in the environment, contributing to a rise in antibiotic resistant pathogens and impacting wastewater treatment processes. CNTs can be used to remove ciprofloxacin from water through adsorption and catalytic processes. When used as adsorbents for wastewater, CNTs can be modified with magnetic nanoparticles such as ferrites 145 or Fe2O3, 146 allowing them to be separated downstream using a magnetic field. Examples of catalytic removal of ciprofloxacin include those where CNTs perform a catalytic function (through the generation of OH radicals 147 ), and where CNTs are combined with other catalytic materials, or are used to support oxidizing compounds in ultrasound-assisted oxidation processes. The co-occurrence of biochar with CNTs seems to be driven primarily by studies which compare the performance of the two materials for their ability to adsorb or otherwise treat environmental pollutants, reflecting the growing importance of this application. To a lesser extent, biochar and CNTs have been combined in composites for heavy metal adsorption and energy storage; biochar can also be used as a precursor for CNT production. Cellulose nanofibers are similar in size and shape to CNTs, and have recently been combined with CNTs in a variety of applications. These include conductive, hydrophilic aerogels made using a mix of cellulose nanofibers and CNT, 158, 159 hydrogels made using a mixture of 2,2,6,6tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibers and CNTs. Cellulose nanofibers and CNTs can also be combined in composite electrodes, where 3D networks of the two materials are used as a support for active materials. The rapid growth of publications involving both MXenes and CNTs is not unexpected, since MXenes have been a rapidly growing field of research since their discovery in 2011. They have been tested in a wide range of applications, including energy, catalysis, and biomedicine. Sensors has been a relatively recent application area for MXenes, with 2017 having been identified as their first significant use in this field. A recent example is a piezoresistive strain sensor based on a composite thermoplastic polyurethane (TPU)/CNT foam with a layer of MXene (Ti3C2Tx) deposited on its surface. The deformation and cracking in both the foam and MXene layers results in a change in resistance per unit strain and is much higher than the sum of analogous sensors made using only a TPU/CNT foam, or a TPU foam/MXene sensor without CNTs. In this example, the CNTs and MXenes are not combined on a microscopic level, but their complementary properties lead to a synergistic effect.