A process for producing a highly oriented humic acid (HA) film, comprising: (a) preparing a dispersion of HA or chemically functionalized HA (CHA) sheets dispersed in a liquid medium, wherein HA sheets contain an oxygen content higher than 5% by weight or CHA sheets contain non-carbon element content higher than 5% by weight; (b) dispensing and depositing HA or CHA dispersion onto a surface of a supporting substrate to form a wet layer, under an orientation-inducing stress; (c) removing liquid medium from the wet layer to form a dried HA or CHA layer having hexagonal carbon planes and an inter-planar spacing d002 of 0.4 nm to 1.3 nm as determined by X-ray diffraction; and (d) thermally reducing the dried HA or CHA layer at a first heat treatment temperature higher than 80° C. for a sufficient period of time to produce the film containing reduced HA or CHA.